Goodman GMP100-4


Old 01-03-17, 04:02 PM
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Goodman GMP100-4

About a month ago the furnace went out at the rental property. Inducer fan would come on, followed by glow light. you would hear the click when it sends the signal to light but it didn't light and glow light would go back out. After 3 attempts it would shut down. Called HVAC guy who said gas valve was bad. He replaced it with a used valve. Ran fine for about 2 weeks then started doing the same thing. Called guy back he says NOT gas valve this; that it needed to be reset. Reset it and it ran fine for 2 days then did the same thing. Called different HVAC and when he came it ran fine. Based on what tenant said repair guy says it is either the fan motor or control board (tenant explained what it was doing and said board was flashing 4 times. Tenant is a HVAC installer (not service tech)). Replaced the control board. I seen it first hand after control board was changed and it is doing what is described above but the board is blinking once after 4 attempts to light. Shutting off power does reset it and it will make 4 more attempts to light and shut down. I know the 1 blink means it went into safety because of excessive failure to light. At my wits end and need advice. 1993 Goodman GMP100-4 gas furnace with heat only. In Virginia where it gets cold one day and warm the next.
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Old 01-03-17, 04:25 PM
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Welcome to the forums.

The voltage needs to be checked AT the gas valve WITH it connected. Upon ignition..... the gas valve is only open for a few seconds if the gas doesn't light.......the igniter will shut back off at the same time as the power is removed from the gas valve.
Old 01-03-17, 05:35 PM
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This appliance is controlled by the thermostat. Within this section, the term lockout is referenced. This lockout is a "soft" lockout which will reset after one hour. It is the obligation of the installer to educate the user on the proper use of the thermostat and the sequence of operation in both the heating and cooling modes. It is also important that any repair or service be performed by a QUALIFIED service person, not by the user.
The furnace control checks for an open main limit (this limit is in the normally closed ). If the limit is open, the furnace will remain inoperable until the limit is closed. During an open limit the circulating air blower will be energized. The status light will blink four (4) times. The room thermostat reacts to a demand for heat.
The control will then check to insure that the vent pressure switch is open. If, at this point, the vent pressure switch is closed the control will blink two (2) times and will remain inoperable until this situation is corrected.
The venter blower is energized.
IO-151 18
The vent pressure switch will close when it detects a pressure in excess of it's setting. If the pressure switch fails to close the status light will flash three (3) times. The sequence cannot continue until the pressure switch closes. The flame rollout switches are then checked to assure that they are in the closed position. After a pre-purge of about fifteen (15) seconds the electronic ignition device will be energized. After a slight delay the gas valve will open if the flame rollout swithches are closed. The burners will ignite and the flame sensor will detect the presence of flame. The ignition device will deenergize. If the sensor does not detect the burner flame, the gas valve will close and the ignition cycle will be repeated for a total of three attempts. If, after the third attempt, the presence of flame is not detected, the furnace will go into a lockout condition for one (1) hour. It will then repeat the ignition cycle. This one (1) hour lockout and retry will occur indefinitely. Thirty (30) seconds after the main valve is energized the circulating air blower will be activated. The furnace will remain in operation until the demand for heat is satisfied. Once the demand is satisfied the venter will shut off, and the circulating air blower will shut off after the field selectable time off is attained. The furnace will remain dormant until the next demand for heat.

This is the sequence of operation for your furnace.

I hope this helps a little.
Old 01-03-17, 09:36 PM
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I don't know spott..... that certainly didn't clarify things.

In re-reading the opening post..... the OP mentions the igniter heats but the gas won't light. Then a 4 flash code is seen. These are two completely different problems.

The board will not go into startup if a limit is open or tripped. The 4 flash code is usually seen several minutes after the burner is lit signifying an overheat problem. A "fan" problem was also mentioned. If this was the main blower..... yes..... you would get a 4 flash code if the blower failed BUT the burner would have had to have been lit.

The igniter on that furnace will not glow unless everything is ok. Therefore... I stand by what I said and the voltage out of the control board needs to be monitored. My opinion.... the old gas valve was fine. You have a control board problem or more likely an intermittent connection on the connecting plug on the control board.

Gas valves are extremely reliable.

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