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Thermostat Not Working Properly

Mark1978 Member Posts: 1
Thermostat type Honeywell RTH6400 Series.
When I have my program set for the heat to come on to 20 it doesn't come on when the room temp falls below 20. The thermostat reads that the heat is on (as per the pic) but the furnace is definitely not on. What I have to do is manual adjust the requested heat temp below the room temp to turn off the heat on sign (relay) on the thermostat. The thermostat will then click off, I then turn the heat setting back to the desired temp and the furnace comes on without issue but will only raise by 2 degrees and then I manual have to repeat the same thing over.
heat.jpg 294.5K


  • Jamie Hall
    Jamie Hall Member Posts: 21,117
    How's the battery?
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Fred
    Fred Member Posts: 8,541
    Are sure you have your schedules programmed correctly. The "Temporary" Heat setting will hold the set temperature only until the next scheduled program. The "Heat" sign on the display is only an indication that you have selected the Heating system as opposed to the "Cool" system or one of the other options. Doesn't mean that the furnace should be running at that particular time.
  • BobC
    BobC Member Posts: 5,401
    I have that same thermostat, I notice it says "HEAT ON" in one of your pictures the system should be on at that time. Can you hear the thermostat relay click on? I'd try replacing thae batteries to be sure.

    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
  • unclejohn
    unclejohn Member Posts: 1,830
    It is the furnace that is not working properly. When you cycle the tstat the furnace resets and then restarts. There may be and error code on the furnace control. Check that.
    rick in AlaskaEmpire_2
  • ratio
    ratio Member Posts: 3,408
    What unclejohn said. Whenever the stat says "heat on", the furnace should be running. What happens is that for some reason the furnace doesn't light (or goes out), so the safety control locks out until it's reset, by turning the heat off & back on. It sounds like it's time to call a pro.