rolltrain

guyod

Every digital thermostat i seen has batteries. I would look harder. Did you take it off the wall?

Daryl in Nanoose

What kind of thermostat is this and what kind of heat ?

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glennjanie

If it is not battery powered then there must be a 120/24v transformer to power the controls. Transformers fail occasionally and have to be replaced. You can completely disconnect the transformer and use an ohmmeter to see if you have continuity on the high side and the low voltage side.
It that is not the problem I would look for a wire that has lost connection.
Glenn

kok328

Check the primary side of the transformer for 120VAC.
Check the secondary side of the transformer for 24VAC.
If you have 24VAC then your T-Stat could be bad.
Check to see if your transformer has a "reset" button, reset if tripped.
All else fails, I usually turn off main power the unit, power it back on and kick it.

triple D

I dont know what kind of furnace you have, but if it is electric, watch out!Your transformer is probably 240volt. Either way it should be located inside furnace. And there usually is a safety switch on the cover like dome light in car, you might have to depress this to test things. Let us know what you find, and how many wires are in t-stat cable, we might need to use these later.. Good luck KOK328 is dead on on test methods, but make sure your not a electric furn. or you'll want to have meter on 240v...

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jack3140

how are you testing for power? if you try across the thermostat wires you will get nothing because it is only a switch connected in series go to the source ie the transfo god luck

wolfenpr

Maybe you just have to replace the thermostat.

falconbrother

If you have a burned out transformer there is a good chance that the contactor shorted and burned up the transformer. There is no good way to test the contactor. You can get one cheap off of ebay. I always keep a 30amp double pole laying around. Last spring my transformer went and nothing on the system would work. I have AC and gas pack. Check the furnace and find the transformer. Make sure you have 120 coming in and 24 going out. This 24 volts probably powers your thermostat. The 24 also powers the electronic control unit and the call for AC (contactor) on the coil. Once I understood my system it became fairly simple to diagnose issues.