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Steam radiators turned on with thermostat below set point

lawsonkline
lawsonkline Member Posts: 2
in Radiant Heating
I have steam radiator system with some rooms on old pneumatic thermostats and others on hand valves. The system worked properly when turned on a few weeks ago but, the other day all the radiators were hot even though the set point on the main thermostat was well below the room temp. That hasn't happened in the past so I'm guessing it's a tstat issue but wanted to ask before replacing it.

Does that sound like a thermostat issue?

Comments

  • Jamie Hall
    Jamie Hall Member Posts: 24,878
    Well, something is asking the boiler to fire. It could be the thermostat. It could also be a short in the thermostat wiring -- or are there any other controls which can fire the boiler? Like an indirect hot water heater or an aquastat controlling the boiler for domestic hot water?
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • JUGHNE
    JUGHNE Member Posts: 11,279
    Pneumatic systems need air pressure to close valves.

    It you lose the air pressure usually the system reverts to fail safe and overheats.

    Do you have an air compressor in the system and what pressure is in the system.
    ScottSecor
  • ScottSecor
    ScottSecor Member Posts: 902
    I agree with @JUGHNE and @Jamie Hall . Is the compress turned off or has it failed? Is there a tankless coil or outdoor reset control that could also fire the boiler?
  • Intplm.
    Intplm. Member Posts: 2,200
    Is this an older thermostat? Will adjusting the heat anticipator help? Short of replacing the T-Stat?
    It's been a while since I adjusted an anticipator with an amp probe meter.
  • JUGHNE
    JUGHNE Member Posts: 11,279
    Show us a sampling of your various thermostats please.
  • lawsonkline
    lawsonkline Member Posts: 2
    Going to try and reply to the all the comments here:
    Yes - it is an older Honeywell...looks like this:




    The air compressor system appears to functioning normally. It turns on as needed and hold about 13 psi steadily.

    The system appeared to respond this morning when I turned down the set point but, I'm guessing based on what the other comments say is that it is likely the thermostat which needs replacing.
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 16,501
    @lawsonkline

    With a mixture of electric and pneumatic controls it is almost impossible for anyone here to figure out what turns your boiler on and off.

    If the boiler does not run all the time to maintain steam pressure, then for the pneumatic side you probably have a PE switch which is a pneumatically operated electric switch that will turn the boiler on. For the electric side if you have any steam zone valve, they would use the valve(s) end switch to operate the boiler probably used with some control relays as well.

    Would need a lot more information to be able to help.
    ethicalpaul
  • mattmia2
    mattmia2 Member Posts: 10,955
    Is the thermostat secure on the wall? Did it get tilted off level somehow?
  • Intplm.
    Intplm. Member Posts: 2,200
    lawsonkline said:

    Going to try and reply to the all the comments here:
    Yes - it is an older Honeywell...looks like this:




    The air compressor system appears to functioning normally. It turns on as needed and hold about 13 psi steadily.

    The system appeared to respond this morning when I turned down the set point but, I'm guessing based on what the other comments say is that it is likely the thermostat which needs replacing.

    That is the old standby favorite thermostat of all time. The Honeywell T-87F Thermostat.
    It has a mercury switch inside and a heat anticipator.
    As @mattmia says above. Make sure it is securely fastened to the wall. Has it been moved or hit recently?
    At this point, it might be best to change the thermostat. That type ( now offered without the mercury switch) is not terribly expensive and might correct things for you. Why not give it a try?
  • Intplm.
    Intplm. Member Posts: 2,200
    lawsonkline said:

    I have steam radiator system with some rooms on old pneumatic thermostats and others on hand valves. The system worked properly when turned on a few weeks ago but, the other day all the radiators were hot even though the set point on the main thermostat was well below the room temp. That hasn't happened in the past so I'm guessing it's a tstat issue but wanted to ask before replacing it.

    Does that sound like a thermostat issue?

    Here is another thought.
    Pneumatic heating valves fail in the open position. If you have a main valve that has lost its air supply. Maybe the air tubing is leaking or disconnected. This could also cause the issue you are having.
  • JUGHNE
    JUGHNE Member Posts: 11,279
    We would like to see your other tstats, the pneumatic ones and the controls at the compressor also.

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