My heater only turns on if the temperature inside the home is 68 degrees or above. If the temperature inside the home is below 68 degrees, I can hear the thermostat click when I turn on the heater but I get no hot air until inside temperature is above 68 degrees. Once the inside temperature reaches 68 degrees due to daylight or whatever, then the heater turns on and works without a problem and maintains whatever temperature I set as long as it's above 68 degrees. What could possibly be the issue?

  • Is it a heat pump? Could it be the outdoor rather than the indoor temp that reaches a level that makes it work? – Tyson Feb 18 '19 at 1:19
  • I don't know what a heat pump is, but the furnace is Carrier Furnace - 59SP2. Only the indoor temperature seems to matter. If I keep the heater on at 70 degrees, then it works without a problem even though it's 40 degrees outside. =( – HeaterProblem Feb 18 '19 at 1:31
  • Is there an air conditioning system involved, or does the thermostat have an air-conditioner setting? What is your thermostat set to? – Daniel Griscom Feb 18 '19 at 1:33
  • There is an AC system and that works fine regardless of the current temperature. I normally have the thermostat set to heat at 73 degrees. I tried setting it at different temperatures all the way upto 85 degrees but no matter what temperature I set it at, it only works when the home is heated to at least 68 degrees. – HeaterProblem Feb 18 '19 at 2:01

It looks like your thermostat is wired wrong way: call for heat wire is connected to call for cool (probably at furnace side, as you said replacing the stat was unhelpful).

So if temp is above the one you set the heating starts as it 'thinks' it have to cool.

Please post a picture of wiring both sides (furnaces and thermostat)

  • Great thought here. @HeaterProblem, have you checked the wiring from the thermostat to the furnace control board? Are you sure the wiring is correct? – Dave Cripps Feb 19 '19 at 0:16

Seems really odd. I'd try to replace the thermostat with a cheap one to see if it resolves the issue. If it does your thermostat is buggered up. There are ways to bypass the thermostat to check it too but you need to be a little handy. Comment back if you want to know more about testing your thermostat.

  • Thanks for the suggestion but I already tried that and ruled that out because I got the same result even after switching thermostats. =( – HeaterProblem Feb 18 '19 at 2:28
  • Can you please give me some background as to, where you live, how old is the unit and are you aware of any other controls like an outdoor temperature sensor. Also model numbers and pictures will help. – Joe Fala Feb 18 '19 at 2:42
  • I've seen the model from previous comments. Might have to do some testing from the furnace itself. – Joe Fala Feb 18 '19 at 2:46

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