I came down to the kitchen this morning and noticed that the heat in that room was on. I checked the thermostat, and it was set to 68 (there is no off switch on this one) but was registering about 80 degrees. My smart thermometer in that room agreed - 78 degrees. So I went down to the basement and of the 7 or 8 zones, it was the only one on. At first, I thought I would just turn the valve for that one off, but then worried that it might result in a buildup of pressure (since there was no where else for it to go), so I turned off the big red "emergency off" switch to power the whole thing off. I guess I would hope the boiler has a pressure limit auto-off mechanisms, but it was summer and so I thought there was little cost to turning it all off and it eliminates any potential risk.
Here are pictures of the various zones, the boiler unit and a close up of the zone valve for the malfunctioning zone. Edit 1a: I've added some photos of the thermostat itself - it's an old model.
What would cause this? A broken thermostat? Or a broken zone valve? and if it's the zone valve, do I need to replace it with the same model (Honeywell 40004850-001) or can I use a newer model?
Edit 1b: Note: the thermostat is an old-school round one. All the other ones in our house are the more modern digital ones with the standard plug-adapter on the back. But this one looks more attached to the wall, so not sure how easy it is to remove and/or test the wires. Is it easy to remove this kind and replace with the new digital model?
Update: it turns out it was the thermostat. I took it off the wall, and things worked fine. I replaced it with a newer simple two-wire digital heater thermostat, and everything seems back to normal.
