I have a honeywell hz432 and just installed a few NEST thermostats with a common wire and they seem to run fine. I added another NEST E thermostat, but this one didn't have a common wire, and when it calls for heat I notice that it seems to be stuck in a loop where it's cycling the system in some way. I see that as soon as the system ignites the burners ready to send heat, it immediately goes into purge mode and then the whole sequence repeats. I put the old thermostat back on and it seems to run fine.

Does this mean my Nest E is incompatible with my system without a common wire? I read somehwhere that I can jump the fan wire into the common somehow if I don't need to control the Fan independently. The other choice is to run an extra wire from the thermostat into my basement through the walls which would be quite a challenge.

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