I have a Goodman GMP075-3 circa 1994 with B18099-06 control module that has not been firing up reliably. Sometimes I will hear the burners attempt to fire then shut off, cycling several times, and sometimes - more often than not - the burners will attempt to light and the furnace will go right into a lockout mode.

In my unit I have three burners with an ignitor on the rightmost burner and a flame sensor on the leftmost burner.

I've observed that when the tstat calls for heat, the vent blower fires up and after a bit I'll hear a relay click and the ignitor will glow. This stage never fails. Then, I'll hear another click and one of the following scenarios will happen:

1) The rightmost burner will light for about a second then shut off and the system will try this again, up to three time total. Either the system will eventually fire up successfully during one of these attempts or wait for a bit then try the cycle again.

2) The rightmost burner will fire then light the other burners and the flames will burn long enough for the blower motor to kick on then the flames will die, leaving the blower running blowing cold air through the house.

3) The rightmost burner will attempt to light and I will see barely any flame at all (if any) and the system will lockout.

When any of these scenarios happen I don't see any blinking of the red LED on the control board, the only time I see the LED go out is when scenario 3 happens and the system goes into lockout.

In the past I've had scenarios 1 and 2 happen and have found that by cleaning the flame sensor with steel wool the problem is fixed.

That said these problems have been happening with more and more regularity over the last week or so. I've found that I can usually get the system to work again by cutting the power and even removing the cover and lightly tapping on the relays on the control module. I don't know if the tapping is actually doing anything, if the system happens to be resetting itself because of the power cut, or it just fires up successfully through dumb luck.

When the system does fire up it runs without any problems until the tstat reaches temp so I wonder if all of the controls (flame sensor, pressure sensor, rollout sensors, etc.) are OK and I either have bad connections at/on the control board or a bad relay.

Does this sound like a bad control module - is there a way to test it to see if it is bad? If so can I replace my B18099-06 with something newer, like a B18099-13S? I found a couple of suppliers with that model, which their web sites state is a replacement for the B18099-06.

Is there anything else I should be checking?

Update: I noticed that the interface between the induced draft motor and the housing (for the heat exchanger?) was not tight and the motor could wiggle. I was able to tighten each of the screws that hold the motor to the sheet metal about 1/8" of a turn. I also noticed that its pink/salmon colored mounting gasket is very dry and crumbly, it looks like there are cracks and even small pieces of it missing. Could this be causing the problem? I wonder because ever since I tightened up the screws I've had three heating cycles without any problems (*knock on wood*).

Update: For the last two days here in Denver the furnace has been running fine during the day but sometime during the night both Wed and Thur I woke up to a cold house to find the furnace in lockout. Repeated power cycles brought the furnace back online. Any thoughts?

Well at least the relays on your board make the click...
I have 2 goodman units circa '95, each with the same board. Having trouble with one. My induced draft motor doesn't kick on. Thinking it is a bad relay on the board. I think that I will swap boards and see if the unit operates correctly.
Found your dilemma while searching for new board or relay...

Since your motor and igniter 'start', then I'm thinking that one of the safety switches are getting a false positive. Such as a bad flame sensor or the vacuum switch. You mentioned cleaning the flame sensor, wonder if there is a way to test if it is still sensing correctly. Perhaps check the vacuum line. If not enough vacuum then that triggers a shutdown. Make sure both ends of the vacuum tube are not loose.

I think you're right, that something is amiss with the safety controls. I just had a couple of days of problem-free heat and now it's starting to lock out again. I'll either get lockout right after the ignitor is hot and the burner tries to light or sometimes I'll get lockout well after the furnace has been running but before the demand for heat has been satisfied. In every case I never see any blinking LED, it just turns right off. I think it's time to call in a pro.

An HVAC specialist just left and the system is running smoothly now... turns out it was dirty, dusty burners. HE disassembled the three burners, cleaned everything in the burner box, washed out the burners themselves and when the furnace fired up it worked perfectly. No more hesitation in getting the three burners to light and it even sounds better when it fires, the furnace used to struggle at lighting, we'd hear a repeating whoof-whoof-whoof sound. Total was $153 including trip charge.

Thanks for the update calanan. Glad things went smoothly, and for a great price.

I spoke too soon and am looking for more help. The furnace ran fine since I posted until late last night when I woke up to find the house was 59 degrees and the furnace was locked out. Power cycled a few times and got it to work again.

I'm beginning to suspect the gas valve but am looking for advice. I am seeing a clear startup sequence all the way through to the HSI igniting then I hear the gas valve click and the system shuts down within a fraction of a second.

When the system works I see a steady 25.5 VAC at the gas valve. When it doesn't work I see anywhere from 2-10 VAC for the brief moment that the valve tries to open before the system locks out, maybe a fraction of a second.

Once in a while I'll see somewhere in the higher end of 17-20 VAC max, the burners will try to but won't light and the system will continue through the process and activate the blower, which just blows cold air through the house.

Based on the symptoms what else should I be checking? I'm reading posts on various web sites recommending everything from checking gas supply (and sediment traps) to checking voltages at various stages to even replacing the control board or gas valve itself. The problem is so random and unable to be reproduced and I'd like to at least narrow down the cause(s) before buying replacement parts.

You should be getting a steady 24v or there abouts when the gas valve is supposed to be kicking on. It doesn't sound like a gas valve problem, it sounds more like a gas valve power supply problem. Its most likely either in the pressure switch that's in the gas valve circuit, or in the control board. Have to see where you are losing power, or partial power when the valve is supposed to open. Check both sides of pressure switches to see if one side has 24v and the other has less, should both be 24v, (not across the leads mind you, but from each lead to ground.)

Thanks for that, mygirlsdad77. Short story long, I ended up calling a local supply house and talking with someone there who initially recommended getting a new flame sensor but that didn't make a difference. In fact, even after a few dozen attempts I couldn't get the burners to light.

I thought this meant that the control board was flaky but when I called back to see if the supplier had control boards in stock his advice was the same as yours, that I might not need a new board and should try to trace down the voltage drop. First he told me how to let the induction motor spin up then jumper the pressure switch, which I successfully tried and it didn't make a difference, which rules out the pressure switch.

Then he said to start checking voltages at the transformer (steady ~26V) and then through the board and circuits. I decided to work backwards from the gas valve to the first rollout sensor, which showed steady 24V voltage and interestingly the furnace fired right up. I shut it down again to try it again and it worked again. It's frigid here in Denver tonight so I decided to let the furnace continue to run tonight but will try checking to see if it will light without having a voltmeter touching that rollout sensor and/or start checking other safeties as I wonder if this is just dumb luck that it worked while I was checking that sensor's voltage.

This is just plain crazy but I'll tell you, I'm learning a lot about furnaces work in the process!

These intermitant problems can be a real bear. And I never like to replace parts without knowing for sure that the part is bad. You are on the right track. Just keep testing and testing and testing until you find the problem. Good luck, and please keep me posted. Im always interested in hearing what you find.

As Im sure you know, I can only guess so much from here. Without being able to put my hands and testing equiptment on the furnace, when the furnace is actually failing, its pretty much educated guesses on my end. Keep on it, and Im truly wishing you the best of luck. The nice thing is, once you get this solved, you will know pretty much what to look for if you have any other problems in the future, as you will mostly have learned the basic operation of the unit and trouble shooting techniques for further issues.

I found the Installation and Operating Instructions for Goodman controls and thought others might be interested reading the listing of steps the control board takes before heating. I've noted where in the checklist my furnace is failing.

Heating Mode
- The furnace control checks for an open main limit (this
limit is 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.
- The vent pressure switch will close when it detects a
pressure in excess of its 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.
- After a pre-purge of about fifteen (15) seconds, the
electronic ignition device will be energized.
- The flame rollout switches are then checked to assure
they are in the closed position.
- After a slight delay, the gas valve will open if the flame
rollout switches are closed.


This is the step where my furnace fails and when it does it locks out within a fraction of a second of the relay click that opens the gas valve, not the seconds or so that it looks like should be expected as each of the safety controls are checked

- 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.