What is the proper way to check the gas valve on Goodman GMT furnace with a multimeter?

[genek1979]

Hello Everyone,

My Goodman GMT140-5D furnace will intermittently not ignite. What I mean is that the after the heat call from the t-stat, the inducer motor will come on, HSI igniter will glow for 15 seconds, but the burners will not ignite w ith flame. After 15 seconds and no flame, the igniter will shut off and try again, to the same result. This will continue until furnace locks out and will flash 1 continuous blink, which indicates an ignition failure fault co de according to Goodman error code diagram.

This doesn't happen every time, but once every 1-2 days. It seems to mostly happen if the temperature inside the home was higher than the t-stat setti ng for most of the day (days are warmer in Colorado now, nights are still c old) and the furnace was not calling for heat for most of the day.

If I remove the rubber hose from the pressure switch, and blow in and out o f the pressure switch, it will click, so I'm pretty sure it opens ok since I hear those clicks every time.

I've already replaced the igniter (twice), 120V/24V transformer, and the co ntrol board. I also had a an HVAC tech bend the HSI igniter bracket a littl e since he was sure that the igniter was too far from the gas burner and no t sensing the HSI glow. That worked for a couple of days, but then the prob lem reappeared. I also already cleaned the flame sensor rod.

I'm thinking that the problem is either a bad gas valve or wiring (possibly from a bad grounding). I haven't replaced the gas valve yet. I'm thinking if I test the gas valve and it receives 24V when igniter glows, but doesn't open, then the problem is the gas valve. If I don't get 24V to the gas val ve when the igniter glows, then the problem is the wiring/control board/gro und, correct??

Can anyone tell me the proper way to check gas valve voltage? I'm thinking I should be checking continuity (ohms) by touching the gas valve terminals with the multimeter test leads (red test lead to red terminal, black lead t o blue terminal) and the multimeter set the Ohms. If that's the proper way, anything higher than OL is good, correct? Or, is it better to check with m ultimeter set to AC voltage? Or should I remove the wires from the gas valv e terminals and check with AC voltage? Again, I'm trying to see if the gas valve is actually receiving 24V from the control board...

Any other suggestions, ideas are greatly welcome...

[trader_4]

is that the after the heat call from the t-stat, the inducer motor will com e on, HSI igniter will glow for 15 seconds, but the burners will not ignite with flame. After 15 seconds and no flame, the igniter will shut off and t ry again, to the same result. This will continue until furnace locks out an d will flash 1 continuous blink, which indicates an ignition failure fault code according to Goodman error code diagram.

ly happen if the temperature inside the home was higher than the t-stat set ting for most of the day (days are warmer in Colorado now, nights are still cold) and the furnace was not calling for heat for most of the day.

of the pressure switch, it will click, so I'm pretty sure it opens ok sinc e I hear those clicks every time.

control board. I also had a an HVAC tech bend the HSI igniter bracket a lit tle since he was sure that the igniter was too far from the gas burner and not sensing the HSI glow. That worked for a couple of days, but then the pr oblem reappeared. I also already cleaned the flame sensor rod.

ly from a bad grounding). I haven't replaced the gas valve yet. I'm thinkin g if I test the gas valve and it receives 24V when igniter glows, but doesn 't open, then the problem is the gas valve. If I don't get 24V to the gas v alve when the igniter glows, then the problem is the wiring/control board/g round, correct??

Sounds correct to me. That is how I would diagnose it.

g I should be checking continuity (ohms) by touching the gas valve terminal s with the multimeter test leads (red test lead to red terminal, black lead to blue terminal) and the multimeter set the Ohms.

That would give you the resistance of the valve, but that's all. And you don't know what the proper resistance is, etc.

If that's the proper way, anything higher than OL is good, correct? Or, is it better to check with multimeter set to AC voltage?

Check with meter set to AC, leads on the valve terminals, with the furnace at the point the igniter is glowing.

Or should I remove the wires from the gas valve terminals and check with A C voltage? Again, I'm trying to see if the gas valve is actually receiving

24V from the control board...

[Stormin Mormon]

Most gas valve, you can touch your VOM lead tips to the push on terminals that power the gas valve. With call for gas, should read between 23 and 29 VAC, in that range.

You might also check for blockage of the flue pipe, might not be enough combustion air flow.

[trader_4]

:

n is that the after the heat call from the t-stat, the inducer motor will c ome on, HSI igniter will glow for 15 seconds, but the burners will not igni te with flame. After 15 seconds and no flame, the igniter will shut off and try again, to the same result. This will continue until furnace locks out and will flash 1 continuous blink, which indicates an ignition failure faul t code according to Goodman error code diagram.

stly happen if the temperature inside the home was higher than the t-stat s etting for most of the day (days are warmer in Colorado now, nights are sti ll cold) and the furnace was not calling for heat for most of the day.

ut of the pressure switch, it will click, so I'm pretty sure it opens ok si nce I hear those clicks every time.

e control board. I also had a an HVAC tech bend the HSI igniter bracket a l ittle since he was sure that the igniter was too far from the gas burner an d not sensing the HSI glow. That worked for a couple of days, but then the problem reappeared. I also already cleaned the flame sensor rod.

ibly from a bad grounding). I haven't replaced the gas valve yet. I'm think ing if I test the gas valve and it receives 24V when igniter glows, but doe sn't open, then the problem is the gas valve. If I don't get 24V to the gas valve when the igniter glows, then the problem is the wiring/control board /ground, correct??

ing I should be checking continuity (ohms) by touching the gas valve termin als with the multimeter test leads (red test lead to red terminal, black le ad to blue terminal) and the multimeter set the Ohms.

is it better to check with multimeter set to AC voltage?

I should have added, this assumes it's a simple one stage gas valve.

[genek1979]

te:

ean is that the after the heat call from the t-stat, the inducer motor will come on, HSI igniter will glow for 15 seconds, but the burners will not ig nite with flame. After 15 seconds and no flame, the igniter will shut off a nd try again, to the same result. This will continue until furnace locks ou t and will flash 1 continuous blink, which indicates an ignition failure fa ult code according to Goodman error code diagram.

mostly happen if the temperature inside the home was higher than the t-stat setting for most of the day (days are warmer in Colorado now, nights are s till cold) and the furnace was not calling for heat for most of the day.

out of the pressure switch, it will click, so I'm pretty sure it opens ok since I hear those clicks every time.

the control board. I also had a an HVAC tech bend the HSI igniter bracket a little since he was sure that the igniter was too far from the gas burner and not sensing the HSI glow. That worked for a couple of days, but then th e problem reappeared. I also already cleaned the flame sensor rod.

ssibly from a bad grounding). I haven't replaced the gas valve yet. I'm thi nking if I test the gas valve and it receives 24V when igniter glows, but d oesn't open, then the problem is the gas valve. If I don't get 24V to the g as valve when the igniter glows, then the problem is the wiring/control boa rd/ground, correct??

nking I should be checking continuity (ohms) by touching the gas valve term inals with the multimeter test leads (red test lead to red terminal, black lead to blue terminal) and the multimeter set the Ohms.

, is it better to check with multimeter set to AC voltage?

[genek1979]

:

n is that the after the heat call from the t-stat, the inducer motor will c ome on, HSI igniter will glow for 15 seconds, but the burners will not igni te with flame. After 15 seconds and no flame, the igniter will shut off and try again, to the same result. This will continue until furnace locks out and will flash 1 continuous blink, which indicates an ignition failure faul t code according to Goodman error code diagram.

stly happen if the temperature inside the home was higher than the t-stat s etting for most of the day (days are warmer in Colorado now, nights are sti ll cold) and the furnace was not calling for heat for most of the day.

ut of the pressure switch, it will click, so I'm pretty sure it opens ok si nce I hear those clicks every time.

e control board. I also had a an HVAC tech bend the HSI igniter bracket a l ittle since he was sure that the igniter was too far from the gas burner an d not sensing the HSI glow. That worked for a couple of days, but then the problem reappeared. I also already cleaned the flame sensor rod.

ibly from a bad grounding). I haven't replaced the gas valve yet. I'm think ing if I test the gas valve and it receives 24V when igniter glows, but doe sn't open, then the problem is the gas valve. If I don't get 24V to the gas valve when the igniter glows, then the problem is the wiring/control board /ground, correct??

ing I should be checking continuity (ohms) by touching the gas valve termin als with the multimeter test leads (red test lead to red terminal, black le ad to blue terminal) and the multimeter set the Ohms.

is it better to check with multimeter set to AC voltage?

AC voltage? Again, I'm trying to see if the gas valve is actually receivin g 24V from the control board...

Will check this and post the results. Thank You trader_4

[Tekkie®]

Oren posted for all of us...

Did you find the video that shows him how to turn on the m/m?

[Stormin Mormon]

Be interesting to hear back from the OP. Wonder if any Goodmans use two stage valves?

[trader_4]

I would expect that every furnace manufacturer has some two stage units today. Some are continuously variable too.

[genek1979]