Diagnosing Intermittent Heater Lock Outs

Problems related to residential installations.

Diagnosing Intermittent Heater Lock Outs

Postby AP114 » Sun Dec 18, 2011 12:36 pm

I have a 20 year old Snyder-General condensing heater Mod# GUH100A016IN.

Over the last 4 weeks, it has locked out twice. I cannot reproduce the lock out situation.

Here is what I know.
- I notice that there is a problem because the house gets cold
- I go down to the heater and the inducer blower is running
- The diagnostic light is flashing on the White-Rogers #50E47-140 control (just flashing continuosly, no numbered flashes)
- I turn the power off and turn it on again and everything works just fine for a week or two.

Any suggestions on how to troubleshoot this problem?
AP114
Minimal
 
Posts: 2
Joined: Sun Dec 18, 2011 12:27 pm

- Diagnosing Intermittent Heater Lock Outs

Postby Freon » Sun Dec 18, 2011 3:28 pm

If it were a flame sensing issue I would expect a lockout AND nothing running. The fact your inducer is running is not expected on a normal lack of flame lockout.

Since it's intermittent it will be a PITA to diagnose. Here's a description of how your control should - *.*/wrdhom/pdfs/instruction_sheets/0037-4836.pdf

It seems the lockout will vary in length which implies that, after so many minutes, it will try to relight again. So I would suspect when you hear the inducer, it's trying to light the furnace. If you can, observe what happens when you're there. Does the ignitor glow bright red to white? Can you hear the gas valve opening? If you're uncertain how this should look and sound, turn off the furnace and then when you turn it back on, watch as it lights. It is possible you have a flame sensing problem albeit a very intermittent one. You may also have an inducer pressure issue so check the flue to be sure it's clear.
Freon
Most Valued Contributor
 
Posts: 681
Joined: Sat Jun 18, 2011 11:26 am

- Diagnosing Intermittent Heater Lock Outs

Postby AP114 » Sun Dec 25, 2011 9:15 am

Thanks Freon

The way this heater is works is that the inducer motor runs as long as the T-stat calls for heat, so it will only shut off when the T-stat gets satisfied.
When the T-stat call for heat the signal(W) does two -
1- activates the inducer blower relay and provides power to the WR control
2-the T-stat signal(W) also runs through the pressure swith and the high limit switch to the Th connection on the White-Rodgers control

That tells me that if the pressure switch were to open while the furnace is running, it would look the same to the WR control as if the T-stat were satisfied and not cause a lock out. Correct?
AP114
Minimal
 
Posts: 2
Joined: Sun Dec 18, 2011 12:27 pm

- Diagnosing Intermittent Heater Lock Outs

Postby how » Sun Dec 25, 2011 3:23 pm

When you find a furnace that has locked out without a logical diagnostic led code showing it usually means that the board is faulty or you have a poor ground connection anywhere from the board to the house service.
how
Most Valued Contributor
 
Posts: 87
Joined: Sun Nov 27, 2011 9:07 pm

- Diagnosing Intermittent Heater Lock Outs

Postby Freon » Sun Dec 25, 2011 5:22 pm

"That tells me that if the pressure switch were to open while the furnace is running, it would look the same to the WR control as if the T-stat were satisfied and not cause a lock out. Correct?"

I agree. The WR control has no idea what is going on with the inducer other than it sets a prepurge time assuming all is well with the inducer (seems crazy but that's how it seems). I assume you have looked at the furnace schematic and see how the pressure switch is wired. Therefore the only thing I can think is the flame sensor is dirty or the WR control is flakey.
Freon
Most Valued Contributor
 
Posts: 681
Joined: Sat Jun 18, 2011 11:26 am


Return to Residential