# Random malfunction on Rheem furnace.



## Raindem (Jan 14, 2022)

Hello.  I have a 10 year old 5-ton Rheem Classic combo unit.  For the past couple of years I've dealt with an intermittent no-heat situation.

Here's what it does.  In the morning, when the heat is supposed to turn on, the inducer will start and the the spark igniter will click a couple of times, then it shuts down and won't retry until power is reset.  The burners never actually light.  There are no error codes.  At some point later in the day, late morning or early afternoon, the furnace will start working normally.  At that point it will function for the rest of the day,  until the following morning.  Some days it works all day.  Other days it doesn't work at all.  But most days it does this "not work in the morning but work in the afternoon thing".  I kept a log of outside temperatures and humidity to see if there was a pattern, but I did not see one.

I've had two different HVAC repairmen out on 5 different occasions but no one can diagnose it.  Sometimes the furnace starts working before they get here, and it's a wasted trip.  But sometimes it doesn't and they are able to go through the troubleshooting sequence.  They've tried bypassing the thermostat, cleaning the flame sesnor and spark igniter, replacing the circuit board, and replacing various sensors (even though there were no error codes).  Blower works fine when directly activated (by thermostat or jumping wires).  They report that voltage is normal at all the key locations.  The filters are new.  I hate to keep throwing parts at it and paying for service calls when no one seems to know exactly what the problem is.  I've tried to troubleshoot it myself also, being that I'm in a position to head up to the roof immediately when it is not working.  I have my tool bag on standby in the morning 

So I'm posting this in the hopes that someone else has encountered this same thing and has an idea on what to look for.   Thanks.

Curt


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## Guzzle (Jan 15, 2022)

Hooking up a 4 or 8 channel analog datalogger or event recorder will probably nail it in one session, if you can rent/buy such a thing.
It will trigger on the fault & display the sequence of events immediately preceding the fault, as if you are looking back in time.

Post a schematic if you can.

Car dealerships have these to track down intermittent problems for their favorite customers.


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## Guzzle (Jan 15, 2022)

Electronic Hobbyist websites may be able to point you to a no-name garage outfit that sells dataloggers, perhaps in kit form. 

A block diagram for it could be analog to digital convertors feeding a memory chip along with a clock pulse generator & various "glue logic," possibly powered by a wall wart.


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## Raindem (Jan 15, 2022)

Thanks for the replies.  But I have no idea what you're talking about.


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## Guzzle (Jan 16, 2022)

Search on "event recorder" or "datalogger".

It does seem that the techs did whatever they could & even if their bosses came out, they wouldn't figure it out either.

And it may be something as simple as a loose connection.  Connections are as much a component as  the other parts.

Maybe an HVAC guy will chime in on how these problems are normally handled.  My viewpoint is from an engineering standpoint.

You could gamble on replacing the control board.

What do you see as your options at this point, besides putting up with it?


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## Raindem (Jan 16, 2022)

The control board was already replaced.  Of course that doesn't mean the new one can't be bad also.  I was just hoping that someone else had already dealt with this, and could pass on the fix.


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## Guzzle (Jan 16, 2022)

There can't be too many faults this basic that you get no error code.

Maybe there is a Technical Service Bulletin out on this problem.
You could write the OEM, I wouldn't bother calling.
If I were the HVAC tech I would have contacted the OEM.  You could ask the previous, now-disheartened techs if they did so.

I had an intermittent no-crank with my '89 Sentra so I wired LEDs to four crucial points & found the problem immediately, but you don't have the option of sitting in front of your furnace watching test points.

With my relay-logic no-computer no-LED 1982 furnace with this problem I'd think a single thing is failing intermittently, probably a loose or tarnished connection.
If tarnish, it could depend on relative humidity.


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## Raindem (Jan 16, 2022)

I asked the last tech if it would be helpful to contact the manufacturer.  He said something like "Yeah,  I guess I could do that", but never heard back from him.  I'll just keep going up there on mornings it doesn't work until the problem reveals itself,  or summer arrives.


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## Guzzle (Jan 16, 2022)

If you really want to get their attention, write to the state agency that oversees these companies.  Sometimes it works.

You have paid to get a furnace that is reliable.  They can't now say that they don't know how to fix this.


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## Guzzle (Jan 17, 2022)

Raindem said:


> In the morning, when the heat is supposed to turn on, the inducer will start and the the spark igniter will click a couple of times, then it shuts down and won't retry until power is reset.  The burners never actually light.  There are no error codes.  At some point later in the day, late morning or early afternoon, the furnace will start working normally.


So you or some geek have a large interval of time where you can make three or four voltage readings to find out what state this furnace has latched itself into.

Prod the spade lugs on the components rather than disturbing the connectors.

If the fault clears while you are doing this, you are close.


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## Raindem (Jan 17, 2022)

Yesterday, the furnace wasn't working in the morning but I had other committments and couldn't check it out.  By the time we got back home it was working.  Today, I'm up bright and early ready to go troubleshooting, and it turns on exactly when it was supposed to.

This will take time.


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## Guzzle (Jan 17, 2022)

It will notify you when it fails.  Have your test points & meter at the ready.

There is probably a schematic/wiring diagram/"ladder" diagram pasted on the inside of a pop-out panel, maybe in the air handler section.


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## Eddie_T (Jan 17, 2022)

If the igniter tries a couple of times then it would seem that either there was either no spark or no gas.


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## Guzzle (Jan 17, 2022)

I think mine has a time-out for this case.


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## Eddie_T (Jan 17, 2022)

Guzzle said:


> I think mine has a time-out for this case.


I would watch the igniter for a spark if accessible.


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## Raindem (Jan 18, 2022)

I have not yet actually seen it try to light, but the repair tech did.  He seemed to indicate that the sparker and gas valve were good, but something else was interrupting the ignition sequence.  Also, he said the furnace is supposed to try to light 3 times before going into lockdown.  But mine is shutting down after the first failed attempt.

The furnace worked this morning so I couldn't do any further troubleshooting.


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## Guzzle (Jan 18, 2022)

It could well be a software bug & the OEM may decide to fix this if the OEM thinks it will come back again & again, to bite him/her self.
Probably S/W is off limits to most, if not all, techs.

I guess the OEM *cannot* say, "Suck it up.", at least not in writing.


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## BuzzLOL (Jan 19, 2022)

After about 20 years, a relay the installers added to my furnace to turn it on when the thermostat calls for heat got so it didn't work without a tap on it the first time I turned the furnace on in the Fall... then it was fine the rest of the winter... but that doesn't sound quite like your problem...


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## Raindem (Jan 22, 2022)

I was able to do some troubleshooting this morning since the heater was not working.  So going back to the start...

It has 120v going in on L1 and L2.  It has 24v coming out of the transformer and going to the circuit board.  The thermostat has 24v going to it and, when the proper connections are made, is sending 24v back to the furnace circuit board.  So power appears to be good.  Filters are brand new.

At the furnace I jump the white to red thermostat wires to call for heat.  The inducer kicks on.  The pressure switch closes (I verified 24v going in and out when inducer running).  The spark ignitor sparks a couple times (I checked it visually) and then everything shuts down.  The burners do not light.  There are no error codes.

I didn't hear the gas valve click (and yes, the gas is turned on).  I try it again and check for 24v at the gas valve.  I only get 1v.  I trace the wire back to the circuit board connector and am only getting 1v there.  According to the schematic, 24v goes from the pressure switch to the gas valve, and I verified 24v at the pressure switch pin on the same connector.  However, the ladder schematic shows, that between the pressure switch and gas valve pins, are 2 open switches labeled "K1".  That label is not in the notes or component codes.  That would appear to be where I'm losing my 24v.  Are those switches on the circuit board itself, or is there something else I can check?  In the attached ladder diagram, the switches I'm asking about are in the lower left of the IFC (integrated furnace control) board.

Thanks


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## Eddie_T (Jan 22, 2022)

IIRC K is used to designate a relay.


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## BuzzLOL (Jan 22, 2022)

Raindem said:


> I didn't hear the gas valve click (and yes, the gas is turned on). However, the ladder schematic shows, that between the pressure switch and gas valve pins, are 2 open switches labeled "K1".


I would expect those are temperature limiting switches on the side of the air ductwork... might be sticking switch or lose connection. My furnace installer rewires so that the inducer fan and igniter are also prevented from working if those switches not 'happy'... ...


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## Guzzle (Jan 22, 2022)

The spark ignitor sparks a couple times. . .and then everything shuts down. There are no error codes.
>Something seems to have timed out.  How long between the sparks & the shut down?

I didn't hear the gas valve click
>No, because the unit thinks it will not have ignition.  This furnace will not blow up your house any time soon.

I try it again and check for 24v at the gas valve. I only get 1v.
>Could be a spurious [not Phantom] voltage.  I guess I’d count 16v & above as “on” and 8v & below as “off”.  
What meter are you using?

labeled "K1".
>A relay, maybe 1 cubic inch in volume.
You could actually draw several schematics depending on which relays are closed or open.  Tedious PITA.

That would appear to be where I'm losing my 24v.
>if the relay coil energizes, the contacts may be bad.
More that 100 millivolts across closed relay contacts [when carrying rated current] mean bad contacts, high contact resistance, worn contacts caused by arcing caused by switching inductive loads [coils].

As of right now, bad contacts are my numero uno guess.



By now, Mr. Holmes, your furnace knows you are not letting this go.  It should be scared!


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## Eddie_T (Jan 22, 2022)

You can check the gas valve by disconnecting its leads and *temporarily* jumpering from 24v transformer listening for click and gas flow.


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## Guzzle (Jan 22, 2022)

Raindem said:


> He seemed to indicate that the sparker and gas valve were good





Eddie_T said:


> You can check the gas valve by disconnecting its leads and *temporarily* jumpering from 24v transformer listening for click and gas flow.


Yes, the valve could be intermittently sticking closed.  Maybe the internals are gummy.

This may account for no bad voltage readings & no codes.  The control board would need to monitor a flowmeter to check for no gas delivery.  It's more concerned about gas delivery when "no spark".

When the symptom shows up again, I'd try whacking the valve firmly with a screwdriver shaft several times while sparking.

Another way would be to "jump start" it with 48vac.  You could wire two 24v 'formers in series, phased properly to deliver 48v, & then whack the valve with that & listen for the click.
Disconnect the valve wires first so you don't feed current back into the furnace.  You are doing this independent of the furnace wiring.
Then sell one trans on e-bay.


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## kok328 (Jan 22, 2022)

Raindem said:


> I have not yet actually seen it try to light, but the repair tech did.  He seemed to indicate that the sparker and gas valve were good, but something else was interrupting the ignition sequence.  Also, he said the furnace is supposed to try to light 3 times before going into lockdown.  But mine is shutting down after the first failed attempt.
> 
> The furnace worked this morning so I couldn't do any further troubleshooting.


The tech is correct about the 3 attempt lockout. so if your is locking out on the first try then it is the control board causing that.
I don't believe 24v goes to the gas valve, I recall mili-volts sent to the valve from the flame sensor when it comes up to temp.
Have any of the techs checked gas pressure at the valve?


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## Guzzle (Jan 22, 2022)

kok328 said:


> I don't believe 24v goes to the gas valve


Mine does, to 3 coils.  I also ohm-ed out the coils.
By now I have a whole notebook on my ancient furnace.

But IIRC there are valves that work on 28 mV & 750 mV.

BTW, at least one tech we had did not know what a SPST switch is.  They just replace modules.  Maybe the company CEO had schooling, the rest maybe learned by OJT.
Goodheart-Willcox publish books on this.

We have got to be close by now.  There's hardly anything left that can cause this.

Re: 28 mV


			https://s3.amazonaws.com/s3.supplyhouse.com/product_files/Resideo-VS820A1336-Product-Overview.pdf
		

Table 4 on page 7 implies that the slightest resistance in the circuit, or tarnished wire, can prevent proper operation.
The valve coil resistance may be 15 milliohms, so at 28mV you'd get almost 2A, enough to move a solenoid armature.  A clamp-on ammeter may work at these low circuit resistance levels.


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## Eddie_T (Jan 22, 2022)

I guess an easy check might be to unplug the wires to the gas valve and probe them during the turn on try to see if  momentary (prolly several seconds) voltage is present during the turn-on attempt.

edit: On second thoughts, since it's intermittent this may only help if it's not present. However if present it will confirm that it's 24v. A clamp ammeter would be better.


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## Guzzle (Jan 22, 2022)

On the 200mVdc scale.


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## Raindem (Jan 23, 2022)

Thanks for the replies.  I'll try to address all the points that were brought up.



> IIRC K is used to designate a relay.



On the circuit board?  Or this a relay integrated with the gas valve?  Is that the same as a solenoid?



> I would expect those are temperature limiting switches on the side of the air ductwork... might be sticking switch or lose connection.



If that's the same as the hi-limit switch, the schematic is showing it separate from the K1 switches



> Something seems to have timed out.  How long between the sparks & the shut down?



Just a second or two



> What meter are you using?



A Fluke DVM.  But it doesn't have a current clamp so I can't do the amp draw tests.



> As of right now, bad contacts are my numero uno guess.



Which contacts?



> You can check the gas valve by disconnecting its leads and *temporarily* jumpering from 24v transformer listening for click and gas flow.



I thought about doing this.  Later on in the afternoon the furnace started working again, and I wanted to get back up there and see what the gas valve voltage was, for comparison purposes.  But I didn't have time to do that.  Maybe tomorrow I can get that value while the furnace is running.



> When the symptom shows up again, I'd try whacking the valve firmly with a screwdriver shaft several times while sparking.



Already tried that.



> Another way would be to "jump start" it with 48vac.  You could wire two 24v 'formers in series, phased properly to deliver 48v, & then whack the valve with that & listen for the click.



Not really comfortable trying this.  I'd lean more towards just replacing it if it is suspect.  But I want to nail this voltage thing down first.



> The tech is correct about the 3 attempt lockout. so if your is locking out on the first try then it is the control board causing that.
> I don't believe 24v goes to the gas valve, I recall mili-volts sent to the valve from the flame sensor when it comes up to temp.
> Have any of the techs checked gas pressure at the valve?



I guess I'm misreading the schematic.  It looked like the gas valve was supposed to be getting 24v.  None of the techs tested for pressure at the gas valve.  



> I guess an easy check might be to unplug the wires to the gas valve and probe them during the turn on try to see if  momentary (prolly several seconds) voltage is present during the turn-on attempt.



I'll try that tomorrow.  Should the meter probes go into each wire, or should I be using another common?


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## Guzzle (Jan 23, 2022)

IIRC K is used to designate a relay.
On the circuit board? Or this a relay integrated with the gas valve? Is that the same as a solenoid?
>>My two 1 cu in relays are mounted on the board.  A massive relay may be mounted on the furnace metal.

A relay
-controlled by the control board supplies current to the gas valve.
-uses a coil to pull in a spring-loaded hinged armature which does the switching of a current too heavy to be handled by the control board.
There are also solid state relays (SSRs).  Pull up some pictures on Google Images.

A solenoid uses a coil to move a spring-loaded cylinder-shaped slug over some distance.


Something seems to have timed out. How long between the sparks & the shut down?
Just a second or two.
>>Don't know what responds this fast.

A Fluke DVM. But it doesn't have a current clamp so I can't do the amp draw tests.
>>OK.

Which contacts?
>>the relay contacts & this guess is now tied with the gas valve being gummed.

>>If the valve is gummed, I’d say 24v for one minute or 48v for one or two seconds should give you a click.

I guess I'm misreading the schematic. It looked like the gas valve was supposed to be getting 24v. None of the techs tested for pressure at the gas valve.
>>When it’s working, check the voltages on the gas valve, one terminal to the other & all terminals with respect to ground.  With three gas terminals this is 6 measurements.
Also measure all the ohms.  The current into the valve will be slightly less than the valve volts/valve ohms.  I=E/R.









						Troubleshooting a Furnace Gas Valve - Fox Family Heating & Air
					

10 Easy Things to Check When Troubleshooting a Furnace Gas Valve Hey guys, today we're going to talk about troubleshooting a furnace gas valve. -




					www.foxfamilyhvac.com


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## maxdad118 (Jan 23, 2022)

I don’t think it’s a bad board, gas control. Maybe try checking for bad/loose connections. I do a fair amount of furnace troubleshooting in my line of work, although I’m not a licensed hvac contractor. It’s intermittent and random, it appears, correct? Was the pilot actually cleaned? Do you have a lazy pilot? If the pilot orifice isn’t clean/clear it may spark but the gas isn’t getting to the spark. I would try manually lighting the pilot hood(where the gas comes out) while it’s sparking to see if it lights.


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## Guzzle (Jan 23, 2022)

^ EZ checks & fast & no risk but you may need a small mirror.


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## Eddie_T (Jan 23, 2022)

There won't be a pilot if it's a spark or glow plug igniter. 

It might be worth checking youtube to see if there are any trouble-shooting postings for your particular furnace or a similar model.


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## Guzzle (Jan 23, 2022)

Mr. Raindem, you're closer to this than we are.
Can you summarize for us
what's been tried, how often & the outcome &
what's left to reasonably try?

BTW, you seemed to have posted your AC schematic.  We need the other one.


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## BuzzLOL (Jan 23, 2022)

"I don't believe 24v goes to the gas valve, I recall mili-volts sent to the valve from the flame sensor when it comes up to temp." -kok328

My gas valve says 24 volts on it...

"But IIRC there are valves that work on 28 mV & 750 mV." -Guzzle

Those low voltages/currents come from a thermocouple... such as on older hot water tanks... on a newer furnace, they would probably signal the computer...

"There won't be a pilot if it's a spark or glow plug igniter." -Eddie_T

On my furnace, the spark ignites a little pilot flame, then it spreads out to the 4 burners... gas valve has pilot and main solenoids...

"If that's the same as the hi-limit switch, the schematic is showing it separate from the K1 switches" -Raindem 

My furnace has more than one set of temperature switches in that location...


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## maxdad118 (Jan 23, 2022)

Eddie_T said:


> There won't be a pilot if it's a spark or glow plug igniter.
> 
> It might be worth checking youtube to see if there are any trouble-shooting postings for your particular furnace or a similar model.


 It could have a spark that lights a pilot, like the 3-wire flame switch type


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## Raindem (Jan 23, 2022)

Another day troubleshooting.  When I woke up this morning the furnace wasn't working.  When I checked it a couple hours later it was, so I went up to check more voltages.  The gas valve voltage is the same as when it was not working, so that's not the problem.  BTW, I misread the multimeter.  It's not 1v, it's 0.1v.  I disconnected the blue wire and checked voltage when it tried to start and I was getting 15v there, which is what someone was saying I should get.  Curiously, as I was checking voltages, the furnace stopped working.  I checked the gas valve & wire voltages again and the same as when working.  Looking again at the red light on the circuit board, it glows solid red when first trying to start up the furnace.  When the furnace shuts down after the brief spark, the light goes out completely and won't come back on until I reset power.  Don't know if that is important, but I thought I'd throw it out there.

In response to today's comments...



> When it’s working, check the voltages on the gas valve, one terminal to the other & all terminals with respect to ground. With three gas terminals this is 6 measurements.


Did that this morning.  Blue wire to common was around 0.1v.  My GV only has 2 contacts.  One contact to the other was around .05v, but the meter kept jumping around.



> Also measure all the ohms.  The current into the valve will be slightly less than the valve volts/valve ohms.  I=E/R.


I'm not that electrically literate.  You'll have to specify which wires or connections I need to check.



> Don't know what responds this fast


Me neither.  I've watched literarally 30 videos on troubleshooting furnaces (including the one you posted).  None of their examples of bad pressure switches, gas valves, hi limit switches, etc, match what my furnace is doing.  It literally sparks for a split second and then shuts down.



> Maybe try checking for bad/loose connections. I do a fair amount of furnace troubleshooting in my line of work, although I’m not a licensed hvac contractor. It’s intermittent and random, it appears, correct? Was the pilot actually cleaned?


Connections have all been checked.  Sparker, Flame sensor, hi limit and flame rollout contacts have all been cleaned.  Connections to circuit board have been pulled off and reinstalled.  No pilot light on this furnace.  Just the sparker.



> It might be worth checking youtube to see if there are any trouble-shooting postings for your particular furnace or a similar model.


None that I could find.  And I think by now I've viewed every video ever made on furnace troubleshooting 



> BTW, you seemed to have posted your AC schematic.  We need the other one.


It included the circuit board connections for the gas,  But that's irrelevant now.  I've attached the rest of the schematic.  Hope you can read it.  My old eyes have trouble.

Again, appreciate all the help on this.  But it is getting frustrating beyond belief.  This problem started last winter.  After the first tech couldn't fix it, the weather turned warm and we didn't worry about it until this year.  I have a feeling this winter will end also without any resolution.  In fact, they'll probably cure COVID before I ever get this furnace fixed.  I can't afford $8k a new furnace right now so we'll have to get by with electric space heaters all over the place.


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## maxdad118 (Jan 23, 2022)

15v is an odd number? Xformers are usually 120/24v? Seems like a weird number to me..


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## Guzzle (Jan 23, 2022)

Raindem said:


> Curiously, as I was checking voltages, the furnace stopped working.


Hopeful, not curious to me. 
You mechanically disturbed something that was loose. 
You now may be able to reproduce the fault whenever you want to if you can retrace your steps. 
You are close.  Connections that are supposed to be insensitive to the pressure of your test prod at sensitive.  If these connections are soldered I'd say it's a solder joint that has become bad.

Or a coincidence, not hopeful.

With 15v, your 40VA transformer [24v @ 1.67A, less voltage at heavier current] may be slightly overloaded.  I'd try to find where all the amps are going.

More to say later.


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## BuzzLOL (Jan 23, 2022)

Raindem said:


> I was getting 15v there


I just turned my furnace on, didn't disconnect anything, reading 25.5 volts AC at the gas valve terminal... between '24 volt' white neutral wire screw and black hot wire screw... maybe your 24 volt transformer has about had it... or maybe a weak connection somewhere's...
I replaced my old 16 volt door bell transformer when it wouldn't ring the doorbell any more...
BTW, I don't think the 24 volt wiring gets connected to ground/furnace metal, both wires an isolated circuit...


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## Raindem (Jan 25, 2022)

I don't understand where I am supposed to be connecting the DVM leads to check for voltage at the gas valve.  There are only 2 wires going to my gas valve, a blue and a brown.  I've checked it from the connected blue wire terminal to common (0.1v), from one terminal to the other with the wires connected (< 0.1v), and blue wire to common with it disconnected (15v).  I get the same results when the furnace is running normally versus when it does the failed start-shutdown thing.  I attached photos of the gas valve and info tag if that helps clear anything up.

Guzzle, unfortunately I can't reproduce the problem.  The furnace will work-not work on its own without anyone touching it, so I doubt anything I did triggered it (later on in the day it started working again on its own).  I won't be able to get back up on the roof until Saturday.  There's a couple more things I want to check but if I don't get a resolution I'm giving up.  This obviously takes someone with more skills than I possess.  Ideally, I'd like to find an HVAC tech who's willing to accept a flat rate fee for _fixing_ it, not just a service charge for showing up and looking. But people have a business to run and I doubt anyone would be willing to do that, especially since I live out in the boonies and the nearest HVAC repair establishment is 40 miles away.


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## BuzzLOL (Jan 25, 2022)

I can't make out much in the wiring diagram. Does it show one or two solenoids on the gas valve? Does it show a separate 3rd return 24 volt path for the red and blue wires? Or do the red and blue loop to each other? The gas valve may sometimes open and sometimes not open with only 15 volts showing...


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## Raindem (Jan 26, 2022)

I don't know how to read schematics.  I was hoping someone else could make sense of it.


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## BuzzLOL (Jan 26, 2022)

Raindem said:


> I don't know how to read schematics.  I was hoping someone else could make sense of it.


Even on my large 27" monitor, I can't make out what the schematic has written on it... maybe you could post a picture of just the gas valve part... 
While the furnace is operating, are you able to take a voltage reading on the 24 volt AC terminals of the 24 volt transformer? (if this style) (Set meter to read AC, not DC voltages)


			https://images.thdstatic.com/productImages/0c705160-85c9-4569-abd6-5b2c923d8337/svn/newhouse-hardware-doorbell-transformers-40tr-64_1000.jpg


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## Raindem (Jan 27, 2022)

Do you want a closeup of the gas valve from the connection schematic or the ladder schematic?

I previously checked the transformer and it's putting out 24v (more like 26-27), whether the furnace is working or not.


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## BuzzLOL (Jan 27, 2022)

How about a picture of both? 
So transformer is 24 volts but only 15 at gas valve? I get 25.5 volts at my gas valve...


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## BuzzLOL (Jan 27, 2022)

Raindem said:


> Do you want a closeup of the gas valve from the connection schematic or the ladder schematic?
> 
> I previously checked the transformer and it's putting out 24v (more like 26-27), whether the furnace is working or not.


How about a picture of both?
So transformer is 24 volts but only 15 at gas valve? I get 25.5 volts at my gas valve...


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## BuzzLOL (Jan 27, 2022)

Raindem said:


> View attachment 27421


Your gas valve has a place on the left to plug two wires onto it, but there is nothing there...


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## Raindem (Jan 28, 2022)

> Your gas valve has a place on the left to plug two wires onto it, but there is nothing there...


That is correct.  There's never been anything  connected there.


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## maxdad118 (Jan 28, 2022)

That looks like a place for a ground.


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## BuzzLOL (Jan 29, 2022)

Raindem said:


> That is correct.  There's never been anything  connected there.


I was wondering if that was supposed to be a better return path for the 24 volts...


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## Raindem (Jan 30, 2022)

Dunno.  The unit had worked fine for several years as currently wired.  And the two HVAC techs that came out didn't seem to have an issue with it.


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## BuzzLOL (Jan 30, 2022)

Raindem said:


> Dunno.  The unit had worked fine for several years as currently wired.  And the two HVAC techs that came out didn't seem to have an issue with it.


The solenoids may be needing more voltage as they age... eventually they won't work at all... 
A lot of 'techs' are just 'parts changers' and don't really know what they're doing...


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## Raindem (Jan 31, 2022)

> A lot of 'techs' are just 'parts changers' and don't really know what they're doing...


I guess that qualifies me then.  LOL.

So let's assume for a second that the unit is wired correctly, let's further assume that the circuit board is sending correct voltage to the gas valve (I checked it again with the unit running the other day and it was 25v).   With the no-start problem generally appearing in the early morning, and with it almost always working later on in the day, the problerm would appear to be ambient temperature related.

Could this cause a sticky gas valve to not function?  Could I test this theory by heating up the gas valve with, let's say, an electric heat gun when it is not working to see if that fixes it?


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## BuzzLOL (Feb 1, 2022)

Yes, you could try that... being careful not to over heat a spot on it and melt the rubber parts inside... although theres not much to 'stick' inside... just some neoprene rubber parts being pressed together... 
You get 25 volts with it running, how about when it refuses to run?


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## Raindem (Feb 2, 2022)

> You get 25 volts with it running, how about when it refuses to run?



It's hard to check voltage in that case because the system shuts down the instant it starts to spark.  I tried checking it this morning but could not get a good voltage reading (< 1v with the meter jumping around).  But at this point I don't if that is a circuit board problem or a gas valve problem.


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## Raindem (Feb 2, 2022)

Tried the heat gun this morning.  No good.

OK, I was able to get good voltage readings on the gas valve today, both when it was working and not working.  The meter probes were at the blue wire at the gas valve, and the brown common wire.  Here are the results...

When unit is working:  At rest voltage is around .4v.  Call for heat comes and the inducer kicks on.  A couple seconds later igniter starts sparking.  Gas voltage goes to 1v.  Once the burners light, the gas valve voltage increases to 25v and remains continuous while running.

When unit is not working:  At rest voltage is around .4v.  Call for heat comes and the inducer kicks on.  A couple seconds later igniter sparks one time and the unit shuts down. Gas valve voltage never changes from .4v.

So still not sure where the problem lies.  The gas valve has to close to complete the circuit, right? 

As requested, I took a couple more pictures of the schematic.  The first 2 are closeups of the gas valve from the ladder diagram and connection schematic.  The other 2 are the same photos a little further out.


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## BuzzLOL (Feb 2, 2022)

Raindem said:


> Gas voltage goes to 1v.  Once the burners light, the gas valve voltage increases to 25v and remains continuous while running.
> 
> + I would expect the voltage goes to 25v first, then the burners light... maybe a delay in the meter showing the 25v... * +
> 
> ...


See comments inserted above...


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## maxdad118 (Feb 5, 2022)

How are the vacuum hoses going to the inducer switches? If they don’t close I don’t think you will get 24v at the control. Have you pulled them off to check for any cracks?


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## Raindem (Feb 5, 2022)

Yes.  I checked the vac hoses for cracks, and made sure the vac port was clear.  I verified that the pressure switch was in fact closing when the inducer kicks on.


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