We have a 3 unit house with hot water baseboard heat fired by an oil boiler. Apt 1 has her thermostat set at 70 but her room temperature is 82 so she set thermostat to 50 and the living room baseboard is hot, and not being controlled by thermostat. All other baseboards in the apartment are working normally as are all baseboards in apts 2 and 3. We changed her thermostat but baseboard is still heating too much. Any ideas on what to check??
Being a 3 unit house you would have to verify the hydronic piping and which zones are which, going to which baseboards, controlled by which thermostats. And then verify how the piping is zoned off, that all zone valves and check valves are functioning. From the sound of it it could be ghost flow.
you would get a good answer asking this on The Wall at heatinghelp.com. They will know all the correct terminology and tell u what specifically to look for.
Most likely the baseboard in question is circulating by thermo-syphon with the circulator pump not running. Hot fluid rises from the boiler and cold fluid falls from the baseboard unit resulting in circulation without a call for heat - common in the one closest above the boiler or with the least complex piping path.
Adding a check valve or even a "trap" to the piping loop can stop that - something to ensure that the pump needs to run for fluid to flow in the loop.
If you have a system with zone valves and one pump rather than a pump per loop it might be a zone valve failure.