Overhead garage gas furnace repair advice

[HemiEd]

I know there are some people on here with some excellent knowledge on these things, so I am going to ask for your help.

I have a overhead gas furnace that my wife had installed for my birthday about 13 years ago, to make it possible for me to work out in the garage this time of year.

Lately, it will not kick on when it is extremely cold out, like 20 degrees in the garage. However, when it is a somewhat reasonable temp, like 32 today, it comes on perfectly.

I am guessing there is some kind of temp sensor, maybe on the heat exchanger, that is no longer functioning in the resistance range it was designed to be?

This unit doesn't have a pilot light, it is electronic start.

Thanks in advance for your help. It would be really nice to have a heater that works when it is cold. :D

[Dayze]

thermal coupler? not sure if they have them on the overhead types...

[allen_kcCard]

Sounds like it is low on antifreeze.

[HemiEd]

thermal coupler? not sure if they have them on the overhead types...

That was my first thought as well Dayze, in fact I took a new one home at lunch. It doesn't have one since it is electronic start and has no pilot light.

Thanks though!

[BlackHelicopters]

Fetzer valve and ball bearings

[mlyonsd]

Did you Google the brand and model? An owners manual might have a troubleshooting guide.

[Dayze]

Fetzer valve and ball bearings

be sure they're 30wt.
25's don't work at all

[HemiEd]

Did you Google the brand and model? An owners manual might have a troubleshooting guide.

I didn't yet mlyonsd, but plan to, but in my haste at the quick lunchtime trouble shooting, forgot to write it down.
My wife is digging out the paperwork on it which should include a schematic, once I get home.

[Radar Chief]

be sure they're 30wt.
25's don't work at all

30. 31, whatever it takes.

[Dayze]

lol.

love that movie

[Moon§hiner]

Without knowing what you have, a newer one should have inducer motor start, pressure switch proves draft, ignition tries, gas valve opens. If flame drops out, clean the flame sensor on the extreme burner from the ignitor.

[Marcellus]

Even if its electric start rather than pilot there should be a sensor that reads the initial flame is lit before turning on the gas. There is some type of thermocouple or temp sensor.

On mine the primary flame lights and a fan comes on for a minute then the gas really hits. I had an issue with moisture getting into mine and it wouldn't fire the intial flame well enough so it kept shutting down before firing up.

Is it cycling like its trying to start or doing absolutely nothing?

Sounds like at really cold temp something in that start up circuit isn't working.

[BlackHelicopters]

220,221...

[kepp]

Sounds like it is low on antifreeze.

Well, there's your problem.

[HemiEd]

Without knowing what you have, a newer one should have inducer motor start, pressure switch proves draft, ignition tries, gas valve opens. If flame drops out, clean the flame sensor on the extreme burner from the ignitor.

It is strictly temp related. In fact, when it was not below zero outside, in the 20s, it would come on, but not quickly. It would take quite some time, maybe half an hour. Then when we hit that -16 to -3 stuff, it wouldn't come on at all. You can hear nothing.

Now that it is in the 30s, it works perfectly.

Even if its electric start rather than pilot there should be a sensor that reads the initial flame is lit before turning on the gas. There is some type of thermocouple or temp sensor.

On mine the primary flame lights and a fan comes on for a minute then the gas really hits. I had an issue with moisture getting into mine and it wouldn't fire the intial flame well enough so it kept shutting down before firing up.

Is it cycling like its trying to start or doing absolutely nothing?

Sounds like at really cold temp something in that start up circuit isn't working.
Absolutely nothing when it is not working, the fan doesn't come on (will with the fan switch) no noise, no nothing. Mine is like yours, when it works right, like today, since it warmed up, the fan comes on for a few seconds, then you can hear the flames hit, and there it goes!

[NCarlsCorner2]

When it's cold outside the unit will cycle on and off more often and that's when the ignition module will fail and lock out, if you turn the unit off it will reset and it could then work again when it's warmer, without looking at the unit I would say you have a bad ignition module.

[Moon§hiner]

Don't know how handy of a guy you are, but if I were called in to fix, first thing I would do `is jumper red to white at the board or with the stat off the wall and see if it still won't fire. There should be 24 volts of potential on a voltmeter when separated. Edit...assuming this is a 24v stat. Some are 110v but I doubt that yours is. Proceed with caution and take power off when doing changes to wiring.

[HemiEd]

When it's cold outside the unit will cycle on and off more often and that's when the ignition module will fail and lock out, if you turn the unit off it will reset and it could then work again when it's warmer, without looking at the unit I would say you have a bad ignition module.

Thanks

Don't know how handy of a guy you are, but if I were called in to fix, first thing I would do `is jumper red to white at the board or with the stat off the wall and see if it still won't fire. There should be 24 volts of potential on a voltmeter when separated. Edit...assuming this is a 24v stat. Some are 110v but I doubt that yours is. Proceed with caution and take power off when doing changes to wiring.Thanks for your help.
Ok, I think we got somewhere from another friend of mine who PMed me.

Last winter the thermostat that I bought at WalMart (Honeywell) to replace the one that went tits up, was a little different. When it is real cold in the garage, it says "LO" on the readout. Maybe it is not intended to operate in these extremely low temps. I am just going to put a toggle switch on it to over ride the thermostat and see if it fixes the problem when it gets colder next time.

[Moon§hiner]

Look at Grainger.com They have low temp stats that are designed for garage/shop apps. if you can't find one locally.

[HemiEd]

Look at Grainger.com They have low temp stats that are designed for garage/shop apps. if you can't find one locally.

Will do, thanks. I had no idea that would have any bearing on it working.

So, if we lose electricity in the house, and it gets real cold, regular thermostats aren't going to fire the furnaces back up when it comes back on?

[A Salt Weapon]

Is this propane or nat gas? Propane can have a regulator freeze up in cold temps and starve the appliance of fuel. Is anything else connected to the gas line?

Also if you remove the access cover you can see the circuit board, should have an led light that will blink a diagnostic code when it fails to fire.

Try jumping the two tstat wires together and see if it fires up.

You can try checking gas pressure with a manometer.
Clean the pilot assembly or if it direct sparks on the burner clean the ignition probe and flame rod using a dollar bill.

That should get you started.