HVAC help - Nest & Viessmann

[mmblz]

If anyone knows HVAC I'd love some help.

Viessmann oil boiler, hot water baseboard radiators. Also connected to a corkscrew heat exchanger for water cycling to swimming pool.

Swapped out an old Honeywell round for a Nest thermostat Tuesday night. Just two wires, red and white. Connected them to Rh and W. Nest came on, seemed happy. Heat came on, all seemed fine until I went to sleep. Around 10am I noticed that although the heat was set to 60 and Nest thought heat was on, the actual temp was 52 and not rising. Went home and checked and the boiler was not running. The "need reset" light wasn't flashing but I tried reset button anyways. Boiler didn't turn on. Turned off at breaker box, back on, boiler didn't come on. Tried manually turning on the pool cycler for a few minutes, boiler didn't come on. On the boiler itself turned the switch off then on - boiler immediately came on.

Things seemed to work all day yesterday until I went to sleep. First thing this morning, heat was 60, temp dropped from 54 to 52. Boiler not on. Reset button, nothing. Off/on, boiler came on.

It's possible that the new thermostat has nothing to do with it - I'm not usually in that building in the morning. Yesterday I waited a good hour or so to see heat come back but maybe I needed to be more patient?

If anyone knows this stuff and has an idea of what might be wrong I'd love to hear it. We've had the oil company out for other things more times than I'd like to think about recently...