Is it possible that a thermostat operates correct all the time except when it reaches the temperature that is set doesn't maintain that temperature?
I noticed that actually that thermostat gives a signal to the furnace but furnace doesn't turn on but that happens only when thermostat needs to maintain temperature that is set.
Is it possible that thermostat isn't working at that regime (to hold the set temperature)?

labman

The thermostat is simply an on/off switch. Below a certain temperature it is on. That will turn the furnace on, and heat up the house. Once it gets above the set temperature, the switch opens and shuts the furnace off. It has a little bit of a dead area so that it isn't constantly turning on and off. That can be adjusted. The older ones that relied on a bimetal spring and mercury tilt switch wouldn't work right if not level. Round ones are difficult to get level. Newer electronic thermostats can have other problems.

gautamanne

I think its your thermostat..See if you can go to your local Home Depot and get a Rite Temp thermostat and call the RiteTemp hotline and have them help you install. Ask for this dude called david. I had a similar problem and was able to isolate by calling these folks ..Otherwise would have costed me a lot to call the tech.

NorthernHeat

Is this a digital stat? Could there be a heating temperature differential you can change in the user set-up? Is the W wire hooked up to W2 ?

senada

Yes it's digital, but there is no w2 position only w. Anyway I changed thermostat today and will see how it works.

senada

Now I know it's not thermostat. Furnace still acts same. Any suggestions what could be a problem. Furnace is 7 years old & it's Lennox G20.

labman

I still don't quite understand the problem. If the furnace and thermostat are working properly, the heat will cycle up and down. When the furnace is on, it heats faster than the house loses heat. When it gets up to a point, the thermostat turns it off. Then the house loses heat until cool enough for the thermostat to turn the furnace back on. If the range is too great, Northern Heat and I both mentioned adjusting it.

senada

What's happening is that furnace fail to start every time when it reaches set temperature.
It works like this: thermostat gives a signal to start furnace, damper door opens, LED lights turns on, pilot flame shows up, LED light turns off, dumper door remains open, furnace not working. Furnace will never start working even when temperature drops for couple degrees unless I turn off/on furnace on power switch.

NorthernHeat

OK lets start over. What brand, type, age and efficiency furnace/boiler/heatpump do you have?

simshawk

I just posted a similar problem today with the LED displays (User ID: simshawk). My unit is a Lennox Elite Surelight, 6 years old, Nat Gas, using a ritetemp thermostat.

When the desired preset is met, the unit kicks off and will not restart until I perform a manual reset.

Here is my post:

Having the following problem.

Woke this morning and temp in house was 62degs. Check thermostat and it said heating, temp set on 68.

Checked the unit and the diagnostic LEDs were flashing alternatively and slow. According to the Diag Sheet, this is "Watchguard - Burners failed to Ignite".

Shut unit down and waited 15mins, performed a restart and unit was working properly, both LEDs flashing simultaneously and slow.

Temp got to preset value 71 degress and the unit shut down again. Noticed temp went back to about 67 degrees, thermostat was showing heating, but nothing was coming from the vents, and no flame on the unit.

Check LEDs again and saw the same "Watchguard" failure as above. Shutdown unit and performed a restart, heater kicked on, but now the LEDs are #1 slow flash, and #2 fast flash, which according to the status table is "Low flame signal, check flame sensor".

Help, its going to be really cold tonite in MI.

Jerry