Thermostat sometimes doesn't work on "auto"

eyeblazy

I have a Honeywell thermostat, which once in awhile refuses to work on "auto."

I remember reading somewhere (maybe here) about the thermostat unit having to be perfectly "square." It has a fair amount of play on end. I have tried adjusting it various times, but so far it hasn't fixed itself. In the past, it has usually come around, but I don't know what I did.

Any help?

Thanks!

HvacWiz

It only has to be perfectly level if it is a mercury stat, If you have one of those digital hunter stats I would replace it.

eyeblazy

Thanks for the info. Really appreciate the advice. It is one of the digital things. Did you mean to replace with a mercury sensitive thermostat or just "time" to replace it with the same thing?

dac122

Time to replace with the same tstat or get a tstat with more capability. Can't imagine why you'd want to return to mercury.

HvacWiz

What dac said

Yoyizit

Try contact cleaner, if you can find someone who still makes it. 24vac at low current may not really wipe the contacts clean (with arcing) like higher voltages and currents. So, any thin layer of oxide or tarnish will make the switch flaky.

Isopropyl alcohol may also work, but with a contact cleaner spray you don't have to dissassemble the unit.
We used to use carbon tetrachloride but that is banned, probably cause it smelled so good.

eyeblazy

Thanks to my you, my advisers. I appreciate your input.

I fixed the thermostat the old-fashioned way. I banged on the side of the case, and voila! I have fixed many things using this tried-and-true method, but forgot about using it for the thermostat.

I will clean the contacts, as suggested, and shop for a new one at leisure.

Thanks again!