I'm working on an LP gas-fired boiler that is the backup/aux heat for a heat pump system. The heat pump is new this year and the problem started with the installation of the heat pump (maybe just a coincidence).
Here's the problem:
If the thermostat calls for aux-heat in the morning, the gas-fired boiler doesn't come on. The blocked vent switch and/or the automatic flu collar needs to be manually overridden to get the boiler to come on. Once it comes on the safety devices can be put back into their proper configuration and the boiler will operator correctly all day. It'll come on and off just fine holding the temp at 68 (btw, outside time is in the 20s). At night the thermostat drops to a setting of 62, so the boiler is off long enough to cool down completely. In the morning when the thermostat calls for aux heat again, to bring the temp up to 68, the boiler won't kick on until the safefy devices are overridden.
I did the easy thing first. I replaced the blocked vent switch. The old switch could be overridden by pressing the button on the back of it. But, the new one, although it has a button, has to have it's wires shorted to be overridden.
The flue collar usually opens when the blocked vent switch is shorted; however, one time, it didn't until I pulled off the cover, then it opened. As if it knew I was coming after it. :^) Okay, maybe not, but maybe my pulling on the cover freed it from not being able to open somehow.
Maybe the flue collar is sticking at a cold temp. Has anyone seen this happen? Any other ideas?