My Furnace goes out when the Temperature goes below Zero
#1
02-19-13, 04:50 PM
My Furnace goes out when the Temperature goes below Zero
I have a miller furnace Model G5RC. When the Temperature goes below zero it quits working. If I shut the power off to the furnace for a hour it will fire up and run and then quit again till I shut it down and start it again. Any ideas of what it could be. Thanks
#2
02-19-13, 07:46 PM
Banned. Rule And/Or Policy Violation
Take the cover off the burner compartment of the furnace.
Describe the sequence of operation you observe when you turn up the thermostat and the furnace lights up properly, in order and in detail.
Do the same thing when it doesn't light up properly.
Post your observations here.
Most diagnostic procedures begin by carefully observing what is happening, and you are luckey to be able to observe the operation of the furnace when it's working properly as well as when it's not.
Describe the sequence of operation you observe when you turn up the thermostat and the furnace lights up properly, in order and in detail.
Do the same thing when it doesn't light up properly.
Post your observations here.
Most diagnostic procedures begin by carefully observing what is happening, and you are luckey to be able to observe the operation of the furnace when it's working properly as well as when it's not.
#3
02-19-13, 08:08 PM
I don't know all of the proper terms. But the ignitor will light but not the gas burner will not light. The sequence is the same till it comes to the burner lighting. It is like the gas has shut its self off. Could it be in the air exchange. Is it reconizing the cold as carbon monoxide.
#4
02-19-13, 08:33 PM
Group Moderator
The exact sequence of events....
For example if the furnace wont light:
turn thermostat up
draft inducer blower starts (that's the blower up top in the flue)
inducer runs for 30 seconds and then ignitor comes on
60 seconds later ignitor goes out.
for example if the furnace does light:
turn thermostat up
draft inducer blower starts (that's the blower up top in the flue)
inducer runs for 30 seconds and then ignitor comes on
60 seconds later gas valve opens and burner lights
2 minutes later main blower comes on
Don't guess at the problem. If we were standing there we would watch and listen to what the furnace does and we would know what the problem is.
Since we aren't there you have to tell us what is happening.
For example if the furnace wont light:
turn thermostat up
draft inducer blower starts (that's the blower up top in the flue)
inducer runs for 30 seconds and then ignitor comes on
60 seconds later ignitor goes out.
for example if the furnace does light:
turn thermostat up
draft inducer blower starts (that's the blower up top in the flue)
inducer runs for 30 seconds and then ignitor comes on
60 seconds later gas valve opens and burner lights
2 minutes later main blower comes on
Don't guess at the problem. If we were standing there we would watch and listen to what the furnace does and we would know what the problem is.
Since we aren't there you have to tell us what is happening.
#6
02-19-13, 08:44 PM
Group Moderator
Even if you don't time them.....you can approximate the time but the order is what is important.
#7
02-19-13, 09:01 PM
I can tell you the order of sequence is
draft inducer blower starts
the ignitor glows
the ignitor glows for awhile and then it turns off
after a few seconds the process will start over again
The ignitor will glow and then shut down again. It keeps repeating the cycles.
draft inducer blower starts
the ignitor glows
the ignitor glows for awhile and then it turns off
after a few seconds the process will start over again
The ignitor will glow and then shut down again. It keeps repeating the cycles.
#8
02-19-13, 09:52 PM
Group Moderator
Perfect...
Now....you mentioned this only happens when it's real cold.
Two things come to mind....gas valve and gas pressure.
This Miller is running on propane...correct ?
I can't find a whole lot of info about this unit but I'm pretty sure it has a control board with a diagnostic LED on it. Try locating the control board and see if it has a blinking light on it.
It may be behind an access cover. Also on the back of that access door should be a listing of trouble code plus a schematic of unit.
Now....you mentioned this only happens when it's real cold.
Two things come to mind....gas valve and gas pressure.
This Miller is running on propane...correct ?
I can't find a whole lot of info about this unit but I'm pretty sure it has a control board with a diagnostic LED on it. Try locating the control board and see if it has a blinking light on it.
It may be behind an access cover. Also on the back of that access door should be a listing of trouble code plus a schematic of unit.
#9
02-20-13, 04:29 PM
Thank you for your reply it does have a diagnostic
board on it and I haven't seen the Led blink the few times I have looked. Now if it quits blinking when it starts to cycle again I am not sure.
The furnace is a Natural Gas Furnace.
Yes it only happens when it is cold outside. The temp is usually around 5 below zero.
board on it and I haven't seen the Led blink the few times I have looked. Now if it quits blinking when it starts to cycle again I am not sure.
The furnace is a Natural Gas Furnace.
Yes it only happens when it is cold outside. The temp is usually around 5 below zero.
#10
02-20-13, 04:35 PM
Banned. Rule And/Or Policy Violation
>
After the ignitor glows, the next step that should occur is for the electric gas valve to turn the gas on to the main burners, and then the burners dhould light alomost immediately off the hot surface ignitor.
So it sound like the main burner gas is not turning on ---- is that right? Usually you can hear the gas turn on if it does.
Because the furnace works sometimes but not others, that confirms that all the gas valves are turned on.
The most likely reason that the furnace wont light in cold weather is that you don't have adequate gas pressure to operate the furnace.
Do you have other gas appliances? If so, what are they ands do they operate OK during these cold weather episodes when the furnace wont light?
If you have other appliances that wont operate at that time, it's a srongf suggestion that you have a gas pressure problem.
Do you have natural gas or propane?
After the ignitor glows, the next step that should occur is for the electric gas valve to turn the gas on to the main burners, and then the burners dhould light alomost immediately off the hot surface ignitor.
So it sound like the main burner gas is not turning on ---- is that right? Usually you can hear the gas turn on if it does.
Because the furnace works sometimes but not others, that confirms that all the gas valves are turned on.
The most likely reason that the furnace wont light in cold weather is that you don't have adequate gas pressure to operate the furnace.
Do you have other gas appliances? If so, what are they ands do they operate OK during these cold weather episodes when the furnace wont light?
If you have other appliances that wont operate at that time, it's a srongf suggestion that you have a gas pressure problem.
Do you have natural gas or propane?
#12
02-20-13, 08:13 PM
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If you do see the LED on the board blinking, count the blinks between pauses. Somewhere on the furnace, maybe on the control board cover or control board itself, should be a key to what the blink code means.
#13
02-21-13, 01:46 PM
Banned. Rule And/Or Policy Violation
As Grady suggests, look carefully for any diagnostic lights that may be signaling a problem.
Post the make and model of the ignition control module or circuit boad on the furnace.
Since the other gas appliances operate OK, that suggests but doesn't prove that you don't have a gas pressure problem.
So what should be happening is that after the hot surface ignitor glows, the electric gas valve should turn the gas to the main burners on and the burners should light off the HSI.
Apparently that is not happening reliably.
That suggests that either the gas valve is energized but is failing to open or that the ignition control module isn't energizing the gas valve when it should.
You need to use a multimeter connected across the two terminals of the electric gas valve to see if you are getting 24 VAC being switched on after the HSI heats up.
If you DO get that voltage and the gas valve doesn't open to allow gas to flow to the main burners, you have a bad (probably sticking) gas valve.
If you DON'T get that voltage after the HSI heats up, you probably have a bad ignition control module that needs to be replaced.
(HOWEVER, other things like the pressure switch COULD cause the ignition sequence to be interrupted, so that would need to be checked as well.
Post the make and model of the ignition control module or circuit boad on the furnace.
Since the other gas appliances operate OK, that suggests but doesn't prove that you don't have a gas pressure problem.
So what should be happening is that after the hot surface ignitor glows, the electric gas valve should turn the gas to the main burners on and the burners should light off the HSI.
Apparently that is not happening reliably.
That suggests that either the gas valve is energized but is failing to open or that the ignition control module isn't energizing the gas valve when it should.
You need to use a multimeter connected across the two terminals of the electric gas valve to see if you are getting 24 VAC being switched on after the HSI heats up.
If you DO get that voltage and the gas valve doesn't open to allow gas to flow to the main burners, you have a bad (probably sticking) gas valve.
If you DON'T get that voltage after the HSI heats up, you probably have a bad ignition control module that needs to be replaced.
(HOWEVER, other things like the pressure switch COULD cause the ignition sequence to be interrupted, so that would need to be checked as well.
