Goodman gas valve not working

[Naaman]

I have a Goodman GMP100-3 furnace that will not fire up. It's been giving me problems for a few weeks now but finally quit altogether. Early symptoms were as follows: Draft induction motor would turn on - after a few seconds, the HSI would glow - the gas valve would open and the gas would fully ignite across all four orifices - after 20 seconds or so, the main blower would turn on and immediately the gas valve would close and flame would go out - after another

20-30 seconds the HSI would glow, valve would open, gas ignite and furnace would run it's cycle without occurrence until the next time the thermostat called for heat.

Later symptoms would be similar to the earlier ones (mentioned above) but would include the gas valve closing even after the main blower was running and flame had been burning for several seconds. Now the gas won't ignite at all, even though I can hear the gas valve click.

After three tries, I got a single flash from the diagnostic LED (ignition failure). So, I tried cleaning the flame sensor...didn't help - I tried replacing the flame sensor...didn't help - I tried bypassing all the temp sensors and connecting the gas valve directly to the control board's purple wire (removed from 1st temp sensor [in series])...didn't help.

I'm getting 27 AC volts to the gas valve and am hearing the right (output side of valve) solenoid click when the control board calls for gas. However, I'm not hearing or feeling the left (inlet side of valve) solenoid click. Almost seams like a week solenoid. Are both solenoids supposed to open together? Why are there two solenoids? Is this for safety....to make sure the valve closes....in case one valve sticks open? I's there a way to test this valve further?

Any help would be appreciated.

[Steve]

Here is a source for the service manual for the Goodman GMP100-3:

[Tony Hwang]

Hi, Checked and cleaned flame sensor? Any trouble code on the control board? You said valve is not working, I think not. It is shutting down 'coz something is not right in the chain of sequence in operation.

Very likely flame sensor just needs cleaning. Good rubbing with emery cloth or cotton fabric will do. I think it is first thing to try. Or the hi limit switch is stuck closed maybe but I doubt it. Check it with multi meter. If it keeps this up/down cycle few times, it'll lock up. To reset it turn the power to the furnace off, wait a little bit and turn it back on. Otherwise it'll be in lock out state for couple hours.

[trader4]

I haven't debugged one of these myself, but it seems like you have the basics covered. If the gas valve has the proper voltage on it and the gas isn't flowing, then either it's a bad valve, pipe leading to it is plugged, etc. It's not a sensor problem.

As to the part about two solenoids on the valve, is this perhaps a two stage furnace?

[Tony Hwang]

Hi, If it is 2 stage valve, 'stat can be configured as 1 or 2 stage operation. For testing configure it as 1 stage and see what happens. Valve is opening for sure that is why you get flames. It is not staying open. Again nothing to lose, check and clean flame sensor. Again, no trouble code?

[Naaman]

It's a one stage valve (only two wires connected to valve [hot & ground]) but it appears to have two solenoids. Already tried cleaning the flame sensor with steel wool. That didn't help so I replaced the flame sensor. That didn't help either. The gas valve does click but no gas comes out. Think I may take the valve apart and see if the passages are clogged. Will update this thread in a couple days.

[Naaman]

Thanks for the reply. Ok, I found out why the one solenoid wasn't opening. When I bypassed the sensors, I removed the jumper wire that bridged the M1 & P3 terminals, in order to make room for the test wire (circuit board purple wire to M1 terminal). I then forgot to replace the jumper wire. After putting the jumper wire back on, the flame is now working. However, I'm still having the original problem of the gas valve closing about 3-5 seconds after the HSI turns off. I did clean the flame sensor and also replaced it with a new one. I am getting 27 volts to the valve while the valve is open and zero volts after it closes. So, it appears that the gas valve is working properly but not sure why I'm loosing the 27 volts. After 3 cycles/tries, I'm getting a single flash on the circuit board, which indicates "Ignition Failure". Maybe my new flame sensor is defective? I may take it back, exchange it and try again.

[Naaman]

I did clean and finally replace the flame sensor. Valve still keeps shutting off

3-5 seconds after HSI shuts off. I think I will return the flame sensor and exchange it for another one. Thanks

[Naaman]

As mentioned in my original post, I did clean and finally replace the flame sensor. However, while installing the new sensor, my screws did strip out when tightening them. Does this need a good connection (good ground) to it's mounting surface? The flame sensor is slightly loose.

[Tony Hwang]

Hi, Sensor has very low o/p voltage, lot less than a volt. meter with mV or miro volt range will see the o/p. Or 'scope.

[Tony Hwang]

Hmm, Two sensor can't be bad. Sensor circuit may be. Or other safety feature is shutting it down. There is a air pressure sensor monitoring draft motor blower. Did you check this guy? Some times loose dirt flopping up/down plugs up that plastic tubing.

[Tony Hwang]

Hi, Sure just like a thermocouple. Dealing with very low voltage(current)

[CRNG]

On Thu, 28 Nov 2013 19:44:02 +0000, Naaman wrote in Re Goodman gas valve not working:

Sounds like you may have a leak in your flame-tube (fire) box. This is where the gas burns. Outside the flame tubes is where the air flows, picking up the heat and bringing into the house distribution ducts. There are sensors to detect leaks. Leaks would allow gas and combustion products to leak into the ducts, so if a sensor thinks there is a leak, it shuts the gas. If your unit is more than 10 year old, this may be the problem.

[trader4]

Why do you have him screwing with sensors, when he says he gets voltage on the gas valve, it clicks, but no gas? That is not a sensor problem. It's a problem with the gas valve, or blockage in the gas line, etc.

[trader4]

Good grief. You had voltage at the gas valve. You heard it click, but gas doesn't come out. That isn't a sensor problem. I suggest you get a pro in.

[trader4]

Based on the new info, I agree it now looks like a sensor or control issue.

Seems very unlikely.

Sensor circuit may be. Or other safety feature

That could be a possibility. He really needs a circuit diagram to see what sensors are involved. Checking the vent pipes for obstructions would be a simple thing to check too.

[bud--]

The service instructions, from Steve's post, appear to be:

You may already have them

According to the instructions 1 flash indicates "ignition failure", which you said, with causes of gas flow gas pressure gas valve flame sensor

Since the burner lights, the gas related items shouldn't be the problem.

The flame rod needs to be in the flame. I think you want the outer cone of the flame. With a loose mounting the rod could be out of position.

The flame needs to contact the burner - it can't lift off of the burner.

The instructions have a test for the flame sensor using a microameter, reading a few microamps. This is a very low current, you may not have a meter that measures that low. The flame rod likely uses "flame rectification" - if ac is applied the current is higher in one direction.

If the flame current is in the specified range the controller is likely the problem.

I didn't look at the circuit - don't know what other sensors are there (like flame roll-out). Some of the other Goodman models will tell you what sensor causes a failure - don't know about yours.

[makolber]

some flame sensor circuits need the furnace to be well grounded electrically because the circuit through the flame completes to the ground.

make sure your power feed ground is good and that the hot (black) and neutral (white) power wires are not reversed someplace.

Mark

[makolber]

but on the on the hand, if the unit always trips off only AFTER THE BLOWER starts, then you might have a problem like rollout that one of the other sensors is tripping off

Mark

[Naaman]

It's WORKING!!! :-D After installing larger screws to fix the loose flame sensor, I tested the sensor with the volt meter. I got zero micro-amps. So I picked up a new control board, installed it and retested. I now have 3-4 micro-amps. Re-connected the flame sensor wire and fired it up. It's been running for over 30 minutes now without a hitch. Thanks to everyone that contributed your input. It would have been another cold night had I not gotten help with this. Much appreciated! :-)