Background: This is a new house, with a boiler system I'm not familiar with. Instead of zone valves, each zone has its own pump (4 zones). There is a fifth pump on the other side of the boiler. Not 100% sure on the controller, but it's a Taco 4 zone.
Problem: Some zones are getting heat without calling for it.
I could feel heat coming off the baseboards in the bedroom last night, and the room was extremely warm. The zone was indicating 72 at the thermostat, programmed to hold 66. Basement was 70, set to 66. Living room was 66, set to 66. Unsure on the 4th zone (didn't want to wake up the kiddo). Went down to boiler room, only the living room zone was calling for heat.
Where do I start with troubleshooting?
Edit: added diagram.
Each zone is using a circulation pump with an internal check valve. Possibly the check is bad? How to test that?
Additional issues identified: air vent is leaking and needs to be replaced. pressure tank reads 0 PSI and leaked water during read. Will try to recharge, but suspect bladder is shot.
Edit: Replaced air vent, so now I am free to start inspecting the zone circulation pumps. Also, the expansion tank actually has some pressure, but my pressure gauge can't read it. I thought it was leaking water, but it was just a few drips. I think it might be ok.
Best Answer
Assuming the thermostats are working, you may be getting residual heat once the thermostat turns off.
Do the pumps have speed controls? Many pumps have LOW, MEDIUM, and HIGH settings. A lower setting may avoid spikes in temperature.
Also, many pumps have mixing valves near them that control the temperature of the water being sent to the radiators in that zone. If you have selective zones that are too hot, you may be able to temper (in this case, lower) the water going to that zone.