# No Power to Thermostat



## THED (Mar 1, 2017)

Hello people that are smarter than I!

We just had a new HVAC system installed in our house(Goodman) and they used a cheap-o Honeywell basic thermostat.

I, being a cool guy, decided I wanted a hi-tech wi-fi thermostat with the touchscreen, etc.

Everything was working fine before I disconnected the existing thermostat but when I finished wiring the new one, no power. Removed new one and re connected the old one, no power.

I'm pretty handy and have tackled many issues from electrical to plumbing but this has me stumped. 

I have no power coming from any of the lines(8 wires, 2 unused) that wire up to the thermostat. What do I check next?

Keep in mind that this is, literally, a brand new system so I doubt it would be a transformer so early. There are no breakers tripped I flipped ALL off and back on multiple times. Still no change.

Please help! Wife is so pissed. haha.


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## nealtw (Mar 1, 2017)

there is an automotive type fuse on the control board in the furnace.


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## THED (Mar 1, 2017)

Thanks nealtw. I'm going to check that when I get home from work and I'll update the thread with results.


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## kok328 (Mar 1, 2017)

This should be a yellow 5amp blade style fuse on the control board.
Always shut the furnace off at the service/convienence swith before working on the thermostat just in case you short the wires.
As far as the new thermostat, sounds like you need a "Common" wire to run it.
Luckily you have two spare wires to accomplish that.
P.S.- old school "basic" thermostat is the type with a mercury ball inside it.


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## THED (Mar 2, 2017)

Hey all!

nealtw hit the nail on the head. The installers had put a 3amp fuse in and, sure enough, it was blown. I replaced with another 3amp and installed the new thermostat and everything is working perfectly.

Thanks for the help!


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## kok328 (Mar 2, 2017)

THED said:


> Hey all!
> 
> nealtw hit the nail on the head. The installers had put a 3amp fuse in and, sure enough, it was blown. I replaced with another 3amp and installed the new thermostat and everything is working perfectly.
> 
> Thanks for the help!



Good call on replacing the fuse with same amp.  I believe Trane uses 5amp but, never replace with greater amp than what is suppose to be.


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