# Please help diagnose a furnace problem!



## romandesign (Jan 4, 2016)

Furnace: Keeprite, 15 year old, Honeywell Q3400A1024 flame sensor/igniter module, Honeywell gas valve.

Problem: blower activates, igniter turns yellow, pilot flame lights up, main burners light up, keep burning for 10-20 seconds and flame out, then after a while ignite again, and flame out after 4-5 seconds. After several tries furnace shuts off with error code of 6 + 2 flashes. The lid describes this code as: "Soft lockout - flame sense lost during run, cycling pressure switch or blocked condensate" - so it lists 3 problems on one code.

Simptoms: After throwing the wall switch off and letting the furnace sit without power for an hour or two - it works for much longer - 15 min to a few hours. It seems that the longer I let it rest, the longer it works after that. If I try to cycle the wall switch off and on right away - it flames out very fast. 

Steps taken: 
- Cleaned the flame sensor, no effect.
- Took off all flexible hoses, made sure nothing is blocking them
- Took off condensate trap (white box on the side of the firnace) - washed it through it openings, some small stiff washed away but it doesn't look like it's blocked, when working there are a little bit of water coming out
- Checked vent pipe - no blockage visible from outsude
- Checked continuity of pressure switch, it closes when blower activates
- Checked amperage flowing from flame sensor - seems to read about 4 microamperes when flame is on, I don't know if that's the right number but it doesn't look wrong.
- I disconnected wires from pressure switch, let the blower activate, then shortened the wires from the pressure switch (emulating closed pressure switch) - no effect, flame comes on and flames out after several seconds. I guess it means the pressure switch is not the problem.
- I invitied the HVAC professional, who basically confirmed and repeated all steps I've done, didn't do anything except shortening one hose (there was a kink) and took $90 for the visit. He said he doesn't think it's the flame sensor, he could change the pressure switch for $250, but the problem can be somewhere else, he can't diagnose it precisely, and he doesn't recommend investing money in this furnace at the end of its life, and just replace it.

I think that by shortening the pressure switch wires (after he left) I eliminated the faulty pressure switch, and all pressure-related problems - because I essentially forced it closed and the flame still was flaming out. I had the same problem last year, and while waiting for the technician to come it sat for 8 hours without power and just started working after that. The problem appeared this time after we went away for 3 days and I lowered thermostat to +16 degrees (Celsius), then put it back on +22C when we came and it failed to heat the house. So I think the only probable cause that's left flame sensor / igniter module - it's not expensive, so I can replace it and see what happens, or the Honeywell gas valve electronics itself, which I won't touch of course. What else can work better after a long cooldown, when pressure switch is eliminated?

Can someone please let me know if my logic is correct? Are there any more steps or tests I can do myself? Am I doing something wrong? Anyone had the same problem - what was the cause and what had to be done?

Inviting more professionals is expensive and as it turned out the first one (highly recommended to me) was unable to even diagnose the problem.


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## nealtw (Jan 4, 2016)

Honeywell Q3400A1024 flame sensor/igniter module
[ame]https://www.youtube.com/watch?v=Es-E4LE3aVY[/ame]
[ame]https://www.youtube.com/watch?v=C1vdUZO52f0[/ame]


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## romandesign (Jan 4, 2016)

The thing is that both valve and igniter/sensor sort of work (see original post) and can light a flame, sometimes even hold the flame for  a while, but then it flames out anyway. I don't know of a method to determine if the flame sensor or gas valve is intermittently failing, but something is...


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## nealtw (Jan 4, 2016)

In the one video , he talks about cleaning the senor but he dosn't say much.
Hopefully a pro will drop by with some better help.


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## romandesign (Jan 4, 2016)

nealtw said:


> In the one video , he talks about cleaning the senor but he dosn't say much.
> Hopefully a pro will drop by with some better help.



I cleaned it pretty well, until it was shiny, but it didn't help at all. Pro guy cleaned it again, no effect...


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## romandesign (Jan 4, 2016)

Here is the photo of the whole thing - with flame working (not for long, as usual):


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## schlich (Jan 5, 2016)

is the flame sensor loose or cracked it could be shorting out or it could be the mother board? i cant see the pic to see whats going on or it could be the flame sensor is not getting good contact with the flame.
can you give me the mod# and ser# this furnace in made by carrier  the guy that came out is right it is on it last leg but he sounds like he was just trying to sell you a new one not fix the problem


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