I’m struggling to find a solution for my furnace. It’s an older Lennox furnace and runs fine. The problem I’m having is that it keeps burning up my thermostats and once it does it won’t let the termostat kick it off. I’ve tried basic 7 day programmable thermostats and nest 2n gen Smart thermostats. Nest has replaced the circuit board a couple of times for me but they end up burning up after a month or so. I’ll come home from work and my condo is 90 plus degrees because it won’t turn off. The wires I have in my furnace are as follows Y1, W1, G, RH. I’ve had multiple HVAC companies come out and look at my furnace and they all say it’s a thermostat issue and then they try to sell me a new furnace. Any ideas on what could be going on here? Is my transformer tripping out the circuit boards in the thermostats.
Nest thermostat gen 2 won’t turn off furnace
thermostat
Related Solutions
I believe you need to move the red wire at the Nest to the Rh terminal. Rh is 24v from the Heating system. The Rc terminal is 24 volts from the Cooling system. Change that around and see if your issue is fixed.
I used following wire mapping from honeywell to nest and I have been up and running for a few days without issue
C = C
Rc = Rc
Y = Y1
G = G
R = Rh
W = W1
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Best Answer
It looks like your nest is wired without the common, so to draw the power it needs, it triggers frequently your heating circuit, doing so, your furnace relay will read a permanent 'call for heat' and won't stop. So, check if in your wall there is a spare thermostat wire (pick black one if present) and connect it to the 'common' side of feeding transformer, so the nest will be able to get power directly and won't have to trigger frequently the heating circuit just to recharge itself anf finally, your furnace will stay off.
To reduce 'thermostat frying rate' an option (if 24V transformer is bundled with your boiler and you can't replace it easly) is to put a second (external) transformer and connect the stat via relays (you'll need 3 relay for DC with 24V coils) in this case the thermostat will have to operate only on 'auxiliary' relays and worst case is that you'll have to replace often only the inexpensive relays.