Goodman GMP125-4 starts sometimes


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Old 12-08-09, 08:40 AM
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Question Goodman GMP125-4 starts sometimes

My furnace will run fine for days and months on end then suddenly not ignite. It was out for 12 hours the other night and the next morning ran fine. It will light on the first try most cycles but then run thru the 3 tries unsuccessfully on the next, only to start again next cycle. the failure code is one blink which is failure to ignite. I had an "expert" look at it and he first told me it was a dirty flame sensor and sanded it. He said that it was locking out. But before he could leave the $115 bill in my hand it shut off while still being 10 below where it was set. Next he told me it was a faulty induction motor. He said it was drawing to many amps and said his office would quote me a new one. I don't have my amp meter at the house to confirm what he said, but during a cycle I slowed the induction motor to cause even more amp draw and possibly cause the furnace to sense the problem and it did not trip any problems. I told his office when they called to sell me the induction motor (for $286 plus an hour labor) that I do not believe this is the problem. So it seem that I get not ignition sometimes and short cycles other times. I think the board is going haywire. any help would be appreciated and sorry for the robust message.
 
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Old 12-10-09, 10:27 AM
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anybody have any help for me?
 
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Old 12-10-09, 11:14 AM
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I'm not too impressed by the competence of the repairman.

Cleaning the flame sensor when you get a flame failure diagnostic code is reasonable, but proposing to replace the inducer motor on such thin evidence is not, in my opinion.

I presume that you can SEE the flame sensor being engulfed by the main burner flames?

With the flame sensor cleaned and the flame failure diagnostic still repeating itself, I'd be suspicious of a bad circuit board or ignition module.

The proper way to test this is first to measure the DC microamps flowing from the flame sensor to the circuit board. Typically there are 4-5 DC microamps flowing ----- that should be checked which requires a good quality multimeter.

Measuring the AC voltage on the flame sensor wire is also a useful check on ignition control.

Also, all the inputs to the ignition module need to be checked to be sure something else isn't shutting off the burners.

These tests might need to be repeated many times in order to be able to observe the problem when the furnace fails to light.

You don't need to wait for the thermostat to turn on the furnace. You can use a jumper wire between the R and W terminals on the circuit board to bypass the thermostat and start the ignition process.

It requires some skill, patience and good judgment to diagnose this kind of intermittent problem reliably. The alternative is to guess that the circuit board or something else is the problem and replace the part and hope, the strategy apparently used by your repairman (although I think his guess of the inducer motor is a poor one).

You might call your repair service back and see if they have someone else with more skill and experience who can help you with this, or call another repair service and take pot luck.
 
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Old 12-11-09, 11:45 AM
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Thanks for the reply. When I get the ignition failure the furnace does not get to the point of creating the flame. It will start the induction motor, power up the HSI, I then can hear the relay click for the gas valve, then fail. Every time I get a flame the furnace will run the cycle. What should voltage and amperage output to the valve be? Could it be that I am sometimes getting improper output from the relay to the valve? To me this seems unlikely.

Board B18099-13
 
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Old 12-11-09, 04:10 PM
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Yes, check to see if you are getting 24 VAC across the wires for the gas valve after the hot surface ignitor has a chance to warm up. Also check to make sure all the gas valves are in the on position.

Do you have other gas appliances that are working normally? That would prove your gas is on.
 
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Old 12-11-09, 04:46 PM
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If you hear the gas valve itself click if you have natural gas -check the gas meter's 1/4 or 1/2 foot dial before and after your cycling test to see if the gas dial moved at all during the few seconds the gas valve should open for, when you hear the click. Then you will know. Some people say at the gas valve click, to try to light it with a barbeque ligher at that moment, while others frown on recommending this procedure.

It's possible you have an HSI that is slowly burning out, and is now weak, and one step away from burning in half. It could be in the marginal stages. You can easily ohms test these. Generally a reading over 100 is considered high enough to warrant changing, although sometimes on certain furnaces they can still fire off the furnace. But they aren't very expensive -$20-30.
 
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Old 12-14-09, 05:24 AM
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Thanks again. I know that the gas supply is adequate because the dryer works fine and the furnace only acts up every once and a while. I will check the voltage to the valve and the resistance of the HSI now and the next time it is faulting out. Also thanks for the tip on checking the gas meter for usage. Hadn't thought of that.
 
 

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