Limited heat in one zone, circulator running, air lock?
We woke up this morning and in our master bedroom, the thermostat read 63 even though it's set at 67. It was single digits cold here overnite but that has happened before and not caused an issue. Our primary winter heat system is an oil fired hot water boiler. The thermostat for the AC/Heat pump (currently that system is off, just still reads temp) also said 63 so it's not a thermostat issue I don't think.
Zone relay is on and circulator feels like it's running (hand on it, get the slight vibration).
I believe our circulators act in a "pull" fashion vs a "push" fashion but I'm not 100% sure (I can't post a picture if need be).
Anyway, the pipe coming out the top of the boiler goes to the valves for the zones in the house. Right up near there, the pipe is really hot as expected (water coming right off the boiler). On the circulator side, it's warm but you can hold your hand on it. I can also keep my hand on the baseboards where I normally can't. It's like some hot is getting through but not well, making us suspect an air lock somewhere in that zone.
Right above the circulator, we have a valve that can be opened to let water out of the zone so we did drain some in to a bucket but didn't hear or see any air coming out. We had that happen in another zone years ago and when you opened the valve, you knew there was air in it because it spit and sputtered. We weren't sure how much water we could take out though and only drained about 2" into a small bucket. This is a long zone because it goes from the basement up to the second floor and the circulates around the master bedroom and bathroom (4 radiators in total). Water automatically gets added to the zone right? So should we maybe drain the whole thing or at least a good bit more and see what happens?
My husband thought that the piping right above the circulator got a bit warmer after we drained some water.
thanks in advance!