Gas and Oil Home Heating Furnaces - gas furnace w/setback thermostat problem

My gas furnace won't turn on when the low temp should be turning on the heater. My thermostat is a LUX 500 series (I had an extra brand new one, that I switched to, but no change), I don't know the brand of heater, it came w/Trane AC unit (2 ton). When the thermostat hits the hi temp, the heater turns off fine and I can set it on hold and the unit seems to work properly. I can also manually override the temp up/down and the heater turns on. So it seems that only the low temp is have trouble telling the heater to turn on. I have the setback thermostat on default 4 degree swing. Any ideas, my heating guy has blown me off the last 2 days, I'm out of town and won't return until midnight Thurs, so wife and child are there.

So it seems that only the low temp is have trouble telling the heater to turn on.
It does sound like a problem with knowing how to program the thermostat.

Can it be left on hold/override?

Did you try LuxPro's website (http://www.luxproproducts.com/) for instructions?

I've had this thermostat for the last 2+ years. I replaced it w/the same exact one due to this problem with the heater not turning on this weekend thinking if it was a faulty thermostat, this would remove the thermostat as the problem.

Hmmm. The only difference might be if you have low heat and high heat controls and the override uses high heat and that works, but the thermostat normally kicks in at low heat.

Does the heat never turn on automatically no matter how cold it gets?
Like tstat at 70, house at 60 and still nothing?

that's pretty much it. I have the low temp set at 63, then when i get up 69. I come down in the morning and the unit says 69 heat, but room temp was 62. I noticed the heat wasn't on, so you can get it to start by turning the heat/off/ac setting to 'off' then 'heat', or adusting the heat temp up/down to 68 or 70 to turn on the heat too. when i left the house last night, i put the thermostat on 'hold' at 69, and my wife said the house was 69 when she got home. so I'm thinking there's something wrong with the relay? on the heater to trigger the low temp setting?

i put the thermostat on 'hold' at 69, and my wife said the house was 69 when she got home.
Good.

The problem you describe sounds vaguely familiar, but I'm drawing a blank.
I'm still thinking that it is some setting on the tstat.


so I'm thinking there's something wrong with the relay? on the heater to trigger the low temp setting?
What I mean is that a call for low-heat (stage 1 power) doesn't work but stage 2 does. It don't know a what temp difference the tstat calls for stage 2. If the thermostat is on 75 does it still get down to 62?

I would start by checking the wiring on the tstat.
Do you have a two-stage furnace?

Sorry,i don't know enough to tell what a stage 1 /2 heater is. How can you tell if you have a stage 1 or stage 2 type?

I would think the wiring on the tstat is fine since it was setup by a heating guy. All i did was replace the front part of the tstat and left the back part of the tstat (this is why I mentioned that I had 2 of the same tstats). You don't think this caused the problem do you?

I would think the wiring on the tstat is fine since it was setup by a heating guy. All i did was replace the front part of the tstat and left the back part of the tstat. You don't think this caused the problem do you?
Yes, the back (subbase) could be the problem, even a loose wire.
You could test by crossing certain screws with the tstat removed.



Sorry,i don't know enough to tell what a stage 1 /2 heater is. How can you tell if you have a stage 1 or stage 2 type?
You either have a single stage or a 2-stage.

If you have a two-stage, the problem could be that stage 1 is disconnected or non-functional but stage 2 works.



Perhaps someone else will recognize the symptoms.

I got back last night, heater seems to be working ok. When I swapped out the existing thermostat to the new one (same identical unit), i used a voltmeter to make sure that the batteries were good (1.50 for both AA's). I decided to check them again, still 1.50 volts but I noticed that the exp. was 2005, so I decided to put in brand new ones anyway. Do you think this might be the problem that causes the thermostat to not turn on when the low temp should trigger the heater? My heater is a Nordyne and the electrical diagrams say it's a single stage heat/cool robert Shaw HS780 hot surface ignition.