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airheatman, HVAC Technician
Category: HVAC
Satisfied Customers: 8267
Experience:  Furnace, A/C and heat pump specialist.
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I had a Goodman GMH81155CN furnace/AC unit installed a year

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I had a Goodman GMH81155CN furnace/AC unit installed a year ago but did not put the furnace into operation because of a lack of propane supply. I did have it converted to a propane configuration. I now have supply and tried to fire it up today but it is not getting propane through the unit regulator valve. The igniter operates fine, but there is no gas supply to the plenum. What should I check for to see why no fuel is being provided through the unit gas valve/regulator?
Hello. My name is XXXXX XXXXX I'll do my best to help. Troubleshooting often requires meters and test equipment. Let's get started and see what we can do.
These units have a little on off switch on the gas valve itself. Lets start by making sure that switch has been turned to ON
Customer: replied 3 years ago.

The switch is on.


Ok, when furnace fails to ignite, look at the led light on the control board and tell me if it flashes, if so how many blinks between pausing
Customer: replied 3 years ago.

Where is the control board located? Do I need to remove the cover to the squirrel cage section? If so, it will take me approximately 15 minutes to get back to you.


Most Goodman furnaces will have a little inspection window to look in to see the flashing led.

Let me ask you this, when the igniter lights, do you hear the gas valve click? and do you have a volt meter to check to see if we are getting 24 volts to the gas valve?

Customer: replied 3 years ago.

OK, I know where the window is located and yes I have a multimeter to check the voltage. I will need to know which terminal to check. But for right now I will go up and recycle the unit and watch for the flashing light I will return in about 5-8 minutes with the result.

Sounds good .We will go from here.
Customer: replied 3 years ago.

I opened the fan door and held the door switch in and cycled the unit. The red light did not flash, stayed a steady weak red, and no sound from the gas solenoid on the valve, there was a click coming from the control board when the igniter cycled on and off.


OK, lets get meter set to ac volts 200. Turn thermostat to call for heat. When igniter lights, see if we get 24 volts between C and PM or C and Hi on the valve
Customer: replied 3 years ago.

Ok this will take approximately 15-20 minutes as I will cycle it multiple times to conform what I am reading.

No problem just come back and let me know if we are getting voltage to valve. We will go from there.
Customer: replied 3 years ago.

Did you get my reply on the voltage? It was 4.0 PM and went to 24 when igniter lit and on HI it was 14 and went to 24

Ok. I just now got the reply. Seems the issue is either in the gas valve or the pressure to the valve. Do you have a gas pressure tester or manometer to verify we are actually supplying at least 11" WC of gas pressure. And did they convert the valve and orifices to LP at installation? Furnace seems to be doing what it should up to the point that valve is not opening.
Customer: replied 3 years ago.

No manometer, and the unit was converted for LP, I guess this then calls for a technician to come and check that? I do not know what one costs, but if it is reasonable, I may purchase one. If the 11" water pressure is confirmed, then I guess the next step is to replace the valve? Your thoughts.

That is correct. Furnace is sending 24 v to valve at proper time, but valve is not opening. This will be because pressure is not right or valve is defective.
Customer: replied 3 years ago.

OK, I am ordering a manometer, or rather a pressure gauge that reads in inches. I will check the pressure and go from there. However, I purchased a "appliance" gas supply line to transition and it came with a connection nipple that had a safety valve integrated. The pressure kept closing that valve until I closed the valve to less just over half open. I am thinking that would indicate adequate pressure. I removed that nipple and installed a full flow nipple and still have the issue of no supply to the burner section. What are your thoughts on that?

Do you have a regulator in the gas line prior to the actual furnace gas valve? It could be that we actually have too high of gas pressure preventing the diaphragm from opening/
Customer: replied 3 years ago.

I have a high press at the LP tank (about 20 in) and a low press (about 14 in )just as the line comes into the building. then a 1.5 in. line to the appliances and the furnace with a run of about 32 ft to the furnace. Only a kitchen stove as WH is electric.


I am curious about the pressure at the inlet of the valve.Why such a large line to furnace. Should only be 1/2" gas line.
Customer: replied 3 years ago.

I am sorry. the line is 1/5, I put a . instead of / I have come to the conclusion that the valve may be frozen. I will wait until I get the pressure gauge and if the pressure is not the problem, will order another valve to replace this one. Will you be available in a week or so to help me through that process? Replacing the valve assy seems to be fairly simple, just take the supply manifold off with the valve and put a new valve on and replace the manifold.

LOL. I was thinking an inch and a half?.
Yes I will be available and look forward to helping and finding out exactly what the issue is.
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Customer: replied 3 years ago.

OK, manometer went off the chart. Called LP supplier who sold me the low pressure regulator and said it was set at 11 in. I removed the regulator, cleaned it out (shook some dirt and crap out) and re-installed the regulator. Service pressure at the furnace is now 11 in. as it was supposed to be. (I think the regulator diaphragm was open and allowed 10 PSI to the furnace valve) but no gas is being delivered to the burn chambers to start. Is the next step to purchase a new gas valve ($100 online) or is there anyway to troubleshoot the gas valve? .

You should have a fitting on the outlet side of the valve to screw a fitting into and attach the manometer. The apply 24v to valve and see what is coming out that side.We should have between ^' and 10" WC coming out.
Customer: replied 3 years ago.

OK, it looks like there are two caps on the valve (white rogers 2 stage) one is low and I cannot make our the other stamping, (hi I am sure) and I will look for the outlet fitting to see if I can hook the manometer up to the valve. I will get back to you as soon as I can..

Ok, the fitting will be a hex or allen screw.Your manometer should have a threaded fitting that will screw in where you remove the cap.
Customer: replied 3 years ago.

OK, voltage is ok, I checked supply at fitting on the inlet side and have 11 in. voltage is still running 4.2 to 24 on one pin and 14.6 to 26.2 on other pin. still no gas to ignition area, everything checks out except the valve will not actuate to allow flow to ignition area.

I suspect the valve will have to be replaced. The high pressure may have damaged the diaphragm in the valve.
Customer: replied 3 years ago.

OK, new development, I put my hand on the valve body as it would cycle when the 24v was applied and felt a slight vibration and heard a faint click as if the solenoid was trying to actuate the valve but it was not opening. And, I suspect you are right, the diaphragm in the valve may have been warped by the hi pressure, (10 PSI) from the tank regulator. I will order one now and get back to you if it does not fix the problem.

Look forward to hearing back, Hopefully this will get you fixed up
Customer: replied 3 years ago.

OK, just a thought, valve on is not a white rogers but a replacement type. What do you think of "replacement parts" that are not the original OEM brand? $100 as opposed to $250+?

Excellent choice. No need to pay for oem parts as long as valve is a compatible valve,I recommend saving the money vs oem.
Customer: replied 3 years ago.

OK, thanks, XXXXX XXXXX order it now. Will let you know what happens and maybe ask some more questions.

I will be here
Customer: replied 3 years ago.

Good news, I replaced the Honeywell valve and the furnace works like it should. I guess the 10psi hit from the stuck low pressure regulator did the original valve in. I am keeping the valve and will try to find a new diaphragm for it and have it as a backup spare.


Thanks for the assistance.


Thanks for allowing me to help..

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