Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

Gas Boiler Heater Turn on When Thermostat does not call for heat

twu1966 Member Posts: 1
Do you know the issue when the thermostat is not calling for heat?
but the boiler is turning and boil the water and the baseboard is hot. I notice the house is very warm.
Thanks in advance if you can advise.



  • pecmsg
    pecmsg Member Posts: 4,838
    What t-stat do you have?
    EBEBRATT-Ed Member Posts: 15,513

    We need to know if your boiler is a hot water or a steam boiler. You mention baseboard which would mean a hot water boiler, but you said boil water which would mean steam.

    In addition, do you heat your domestic hot water (faucet water) off the boiler.
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 7,817
    edited April 2022
    I am very familiar with this issue. I have repaired it many times in my career. If you have a stuck gas valve. then no amount of electrical wiring repairs or plumbing pipe, valve, or pump fixes can solve this problem. But that only happened to me once, on a warm air furnace in by 40+ years in business, so this is probably not the problem you have. It is very rare.

    Another problem could be a wire with the insulation damaged allowing the thermostat circuit to be completed behind the wall even if the actual thermostat is satisfied or even turned off.

    There was a Diner in New Jersey that has a large hole in the wall behind the thermostat. The exhaust fan(s) in the kitchen created a negative pressure zone inside the dining area. Cold air from the hole behind the thermostat was being sucked in thru the hole past the thermostat giving a false temperature reading to the thermostat. The thermostat was not reading the room temperature but reading the outside air temperature that was being sucked in to the room from behind the wall. Electrically the system was working just fine. Sealing the hole in the wall is the solution for this customer

    I think the most common issue I have come across with boilers are valves that are stuck open that allow heated water to flow when flow in not needed.

    There was one situation known as Ghost Flow where heat travels up a pipe while cooler water from radiators travels down the same pipe because the cooler water is heavier than the warmer water. I could not believe that water could flow in two directions in the same pipe... But it can.

    I hope this answer gives you some insight into the many causes to your particular issue. More information about your system, and some pictures can help. The professionals need to know if you have a Furnace, or a Boiler. And if it is a boiler, does the boiler make hot water or steam to heat your home. Those differences will help eliminate some of the speculation.

    Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics