One of three zones of heat only works if another zone is on. (hot water baseboard, paint)

[gm3333]

Hi there,

2002 house with original oil burner/boiler. I have three zones, hot water baseboard heat. I also have an indirect hot water heater (as it was explained to me) that is tied to the boiler. I've lived in the house for three years with regular boiler cleanings and everything has been running fine.


Over the last few months and after much experimentation that I've noticed that one zone of heat (the upstairs), will not actually turn on unless another zone in the hose is already on. The thermostat goes through all the cycles and says its on but nothing happens. I tried to swap the face of the thermostat with one from another zone that I know works, but that didn't seem to help.


Any ideas what would cause this? I'm not looking to solve the issue, but would like to have a general idea of what might be wrong before I call someone down.


There is another symptom that has existed for a long time. I will share here in case it's related. With my indirect hot water heater, if you are on vacation for a while, it will take an extremely long time for the hot water to be hot at any tap/shower. This issue always happens a bit in the winter if the heat is for some reason off on all zones for a while, it might take some time for the shower to get hot water, and generally gets hotter if I turn the heat on. I don't usually notice this as I'm either showering while the heat is on, of I've recently used hot water. I've had a few people check it out when they are here for the annual cleaning, but they can't find anything that's wrong.


Thanks for any help. I am happy to supply photos if needed.

[Rickcin]

Unsure about the water heater, however you should be able to turn on each heating zone and visually see if the zone valves are working. Most of them have a visual indicator and you can manually open the valves as well. Perhaps one is bad or hanging up for some reason.

[thecoalman]

I'm assuming this is zoned with valves. For the thermostats that do not work on call for heat they are likely only operating the valve and not wired properly to engage the aquastat/pump. When the one thermostat correctly wired to the aquastat calls for heat the pump will engage and heat will flow through the open valve. If you look on the side of the boiler there should be square box about 8 inches high and 5 inches across, typically grey and made by Honeywell. This is the aquastat, find the model number. If it's not on the outside turn the power off to the boiler, there is some screws holding the cover on. Remove them, the exposed wires inside carry power but should not be live if you cut the power first. Just be careful. The model number should be on inside cover. Look the manual up and it will give you schematics how to properly wire the system.



There is going to be some metal boxes for each valve/thermostat. typically unpainted and about 4*4*4, they may be right on the valve. They need to be wired to each other and finally the aquastat to engage the pump.


There is some examples here:


https://www.google.com/search?q=wiri...k0nalsGdB2zPM:

There is another symptom that has existed for a long time. I will share here in case it's related. With my indirect hot water heater, if you are on vacation for a while,

This could be related because it will likely have valve operated by thermostatic control on the tank. Same thing could be occurring here where the valve is opening but you are only heating water on call from heat with the one thermostat that is correctly wired to the aquastat.

[K'ledgeBldr]

Ah hah! I see this "problem" all the time! You have a "hot water heater"!!! All you should require is a "water heater".
What I meant to say is- I hear this all the time.

OK! All joking aside- I think coalman has your answer. All thermostats are not communicating with the circ pump.