Furnace question

[odie]

I'm having a small issue with my furnace/thermostat. Thermostat is always set to 70 degrees. For the most part, the furnace keeps it at that temperature with no problems. But on occasion, I'll wake up in the morning or come home from work and the temperature is at 65-66 degrees and the furnace is not running. (Outside temp has been in the 40's all week).
If I turn off the furnace and then back on or set the temperature to 71, then it kicks on and heats the house to 70 or 71.

Anyone had a similiar issue? Going to change the thermostat out this weekend, unless someone else has a fix.

Thanks

 

[txst]

Look at the blinking diagnostic light on the furnace control board before you turn the thermostat off and on to see if there is a code. Sometimes a furnace will lock out on a fault that gets cleared by cycling the thermostat off and back on.

 

[Terra Nova]

Look at the blinking diagnostic light on the furnace control board before you turn the thermostat off and on to see if there is a code. Sometimes a furnace will lock out on a fault that gets cleared by cycling the thermostat off and back on.

Sorry this made me chuckle. A board full of auto techs so the first answer you'll get to any problem is "pull the codes"

He might have an old school furnace with a mercury switch thermostat.

Sorry, can't really offer much help, but assuming it's gas fired I had a sorta similar problem with my gas water heater. The flame indicator would not always read right and it would kick on a few times and them shut off and stay off until I reset it.

 

[signcrafter]

As mentioned most furnaces have a trouble code light built in to tell you what is going on. From there google is your friend. Based on my experiences I would guess that your flame sensor is dirty or out of position and not reading. I had this happen before where the furnace would try to light but the flame sensor wouldn't read that it lit and would shut gas flow off and go into fault. I cleaned the sensor with some steel wood and good to go.

 

[G_P]

So its 66 inside and the tstat is set to 70 and the furnace wont run?
But if its 66 inside and the tstat is set to 71 the furnace will run?

Or does it only start when changed from 70 to 71?

First thing I would do is jumper the thermostat wires at the furnace and see if it turns on and stays on. If it does the problem is in the tstat or its wiring.

 

[odie]

So its 66 inside and the tstat is set to 70 and the furnace wont run?
But if its 66 inside and the tstat is set to 71 the furnace will run?

Or does it only start when changed from 70 to 71?

First thing I would do is jumper the thermostat wires at the furnace and see if it turns on and stays on. If it does the problem is in the tstat or its wiring.

The numbers were just examples. It only kicks on if I turn the heat up at least one degree or turn the unit off and back on.

 

[G_P]

That sounds like a thermostat issue.

Try jumping the wires at the furnace to make it run.

When I worked at HD we sold TONS of digital thermostats. From what I gather they are an item that fails rather frequently.

 

[RECox286]

You need to supply a lot more information...What brand and model

furnace, what brand and model t-stat. Check to see if furnace is

in lockout when it won't run: blower runs constantly on cold furnace.

Uncle Bob

 

[bazar01]

The numbers were just examples. It only kicks on if I turn the heat up at least one degree or turn the unit off and back on.

What type of furnace? Heat pump with electric heat back up, heat pump with second stage gas heat, or just a gas furnace?

What type of thermostat?

 

[theoldwizard1]

Sorry this made me chuckle. A board full of auto techs so the first answer you'll get to any problem is "pull the codes"

But its true !

My furnace has a "ignition sensor". If it does not "see" a hot igniter, it won't open the gas valve. Every couple of years I have to clean the sensor.

 

[danfromsyr]

on an electronic t-stat the bits that regulate the furnace are differant than the bits that it puts up on the digital display.
the furnace side relay may be faulty.
time for a new T-stat. (or possibly T-stat battery)