Goodman GMP only lights sometimes
#1
03-17-19, 08:21 AM
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Goodman GMP only lights sometimes
Older GMP furnace sometimes will call for heat but the igniter stays on for a few seconds then shuts down. Repeat 3 times, no light. Sometimes if I turn the power off or cycle the thermostat it will run fine for the rest of the day. The one flash LED lights on the board.
i have cleaned the flame sensor and even replaced it, symptom is still intermittent.
HVAC Pro site suggests it’s cracked heat exchanger but not willing to accept that yet (as Spring approaches).
im going to put an endoscope in the heat exchanger but not until the outside temp is good one day.
Any troubleshooting tips.
thanks.
i have cleaned the flame sensor and even replaced it, symptom is still intermittent.
HVAC Pro site suggests it’s cracked heat exchanger but not willing to accept that yet (as Spring approaches).
im going to put an endoscope in the heat exchanger but not until the outside temp is good one day.
Any troubleshooting tips.
thanks.
#3
03-17-19, 09:50 AM
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Thanks. Any idea what shouldread? Take reading I series I Suppose? If not to spec would mean bad circuit board or?
#4
03-17-19, 10:16 AM
Member
Before you go any further check the heat exchanger. If it’s cracked your furnace is dead and not worth fixing.
Pull the blower and check the crimp rings from the bottom.
There’s a high chance yours is cracked. Most GMPs are long dead.
Pull the blower and check the crimp rings from the bottom.
There’s a high chance yours is cracked. Most GMPs are long dead.
#5
03-17-19, 12:00 PM
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#6
03-17-19, 01:00 PM
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Pull the blower first. The crimp rings pop off the bottom of the heat exchanger and usually end up laying on top of the blower housing.
#7
03-18-19, 07:52 AM
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Temp as down 5 degrees below thermostat setting this AM so it must have been on a bit last nite but not operating correctly. It’s in the 40’s here.
i disconnected the wires to the gas valve and inserted a voltage meter and pre ignition showed 21-22 volts AC (should be 24 plus?). During ignition jumped up bit to 25.5 volts AC with igniter on.
Voltage seems low.
I reattached the valve wires and of course the furnace came on as it should first time and has functioned well for the past hour.
I noticed my rollof switch is corroded but function and has continuity. My replace it.
Ill probably put some deoxit on the valve contacts, maybe just a poor connection.
ideas?
i disconnected the wires to the gas valve and inserted a voltage meter and pre ignition showed 21-22 volts AC (should be 24 plus?). During ignition jumped up bit to 25.5 volts AC with igniter on.
Voltage seems low.
I reattached the valve wires and of course the furnace came on as it should first time and has functioned well for the past hour.
I noticed my rollof switch is corroded but function and has continuity. My replace it.
Ill probably put some deoxit on the valve contacts, maybe just a poor connection.
ideas?
#8
03-18-19, 08:01 AM
Member
Wires need to be connected for testing.
Like I said previously you need to check the heat exchanger prior to anything else. If it’s cracked the furnace is dead.
Like I said previously you need to check the heat exchanger prior to anything else. If it’s cracked the furnace is dead.
#9
03-18-19, 06:40 PM
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Been working 100% all day. Dunno.
From looking at the flame the heat exchanger is functioning as intended. Satisfied for now that is isn’t cracked.
From looking at the flame the heat exchanger is functioning as intended. Satisfied for now that is isn’t cracked.
#11
03-18-19, 07:19 PM
Group Moderator
i disconnected the wires to the gas valve and inserted a voltage meter and pre ignition showed 21-22 volts AC (should be 24 plus?). During ignition jumped up bit to 25.5 volts AC with igniter on.
There should be 0v on the gas valve until it's time to open. The igniter preheats for approx 30 seconds and then the gas valve is powered with +/- 24vAC. If the burner lights..... the igniter shuts off and the gas valve stays powered. If the burner doesn't light within 7 seconds..... the gas valve and the igniter are powered down for a restart.
Corroded terminals on the gas valve are a common problem.
Corroded terminals on the gas valve are a common problem.
#12
03-19-19, 06:25 AM
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Thanks. Thought it odd that I was reading voltage at rest. Using basic multimeter set at Voltage AC.
Been working fine for last 24 hrs. At some point (once Spring kicks in) I will inspect the heat exchanger for cracks.
Been working fine for last 24 hrs. At some point (once Spring kicks in) I will inspect the heat exchanger for cracks.
#14
03-19-19, 03:39 PM
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1 Led, working flawlessly since I disconnected/ reconnected the gas valve electrical. Also tapped the rollout switch.
Or or or the other I suppose.
Or or or the other I suppose.
