No heat from gas furnace

[illuminance]

I have a Goodman gas heater. It is 6 years old. Never had any previous problems. This week when I turned on the thermostat, it blew only cold air. The unit uses a Gemini White Rodgers 36G54 gas valve.
I checked the gas line coming in to the valve and the gas is coming in strong. I called Pacific Gas & Electric and the technician came out and said there is gas to the valve. The pilot is lit. The problem, he said, is the valve is bad (not opening). I was surprised considering it is only 6 years old. However, I got a replacement valve (brand new, same kind) and installed it. The problem has not changed at all. Unit turns on and runs, just blows cold air. - There is gas to the valve. Okay, so I think the PGE tech was wrong and I just blew $80 replacing a valve that probably was operational. What should I check for next? Any help appreciated?

[Freon]

You say the pilot light is visible. I will then assume you have a standing (always on) pilot. If you have another type of pilot, like an intermittent pilot that lights via a spark when there's a need for heat, let us know.

Have someone call for heat while you are at the furnace with paper and pencil. Write down everything you see and hear as the furnace tries to light and give you heat. Also post the Goodman model number.

[illuminance]

Sorry, should have posted this info to begion with...It is a Goodman GMH950453BXAA...Auto Igniter Pilot. The PG&E tech *said* the pilot was coming on, he checked for it and said it was good....if that is the case, with a gas supply, functioning valve, and spark, what else should I be looking for? Thank you all and have a Merry Christmas.

[Freon]

You have a Hot Surface Ignitor ( "pilot") ignition. That means the HSI will be energized and glow white hot thereby igniting the main gas burners.

You need to go and observe what is actually happening. Have someone call for heat at the thermostat while you look at the burner assembly.

You should first hear the smaller inducer motor start, establishing the proper draft. If the pressure is correct the HSI will be energized and you should see it glow white hot. If that happens then the main burner should come on and you'll heat the gas valve click open.

Tell us what you see and hear.

[illuminance]

Hi Freon, thanks for your help...

It seemed like the gas valve WAS opening and the pilot coming on. But no heat. I *gave up* and called an HVAC tech. So he came out and -
1. Low voltage to the gas valve approx 27V
2. Could hear and feel the control valve opening
3. Saw the pilot come on, gas valve opened
4. The gas supply to the valve is strong

Then, the pilot would fade off because, according to the tech, no gas making it to the pilot. The LED diagnostic is showing "1" which indicated lockout.

In the end, the tech could not diagnose the problem and said he would call Goodman tech later. The saga continues...

[Freon]

It seemed like the gas valve WAS opening and the pilot coming on. But no heat. I *gave up* and called an HVAC tech. So he came out and -
1. Low voltage to the gas valve approx 27V
2. Could hear and feel the control valve opening
3. Saw the pilot come on, gas valve opened
4. The gas supply to the valve is strong

Then, the pilot would fade off because, according to the tech, no gas making it to the pilot. The LED diagnostic is showing "1" which indicated lockout.

First, 27 volts AC is more than enough for the gas valve. Most transformers are rated at 24 volts AC.
Second the HSI stops glowing because the flame sensor circuit is telling the control board it does not see a main burner flame. This behavior is part of the safety system.

Can you hear the gas valve open and the whoosh of gas flowing into the burner? If you can then the HSI is not hot enough to ignite the burner and you need a new HSI.

If you don't hear the whoosh after the gas valve opens, post the gas valve make and model number

Read pages 38 and 39 here from the installation manual to understand -
w w w . alpinehomeair . c o m Slash related slash IO DASH 299P 10 DASH 2012.pdf

[illuminance]

Ok, the problem is now solved. Unfortunately, it took an $84 service call to solve it. The tech diagnosed the problem right away and fixed it in about 7 seconds. All it took was.....a small cup of water! There is an external reservoir that needs to be kept filled. Acts like a trap under your sink. Poured the water in, furnace fired right up. Boy do I feel stupid.

[Freon]

Don't feel stupid. I am still puzzled. If you look at the drain trap do you see any wires possibly connected to a float switch. I ask because in the installation manual they do say to fill the trap but given it's connected to the flue side of the heat exchanger having water in it isn't critical. And there's no mention of any electrical connections to a float switch. The only explanation I can think of is when there's no water in the trap, the connection from the flue to the ambient air affects the draft pressure. But if that were true, the furnace should never even try to light.

I am glad you're back with heat. Thank you for telling us what was wrong.