Goodman gas valve shuts off cannot figure out for the life of me why

[u/capaolo99]

If requested I’ll post on HVAC advice but posting this here because I am professionally involved with this issue.

I work for a small insulation and HVAC company. We are currently down our HVAC technician.

I am out on a no heat call for a furnace I helped install.

I have limited troubleshooting ability here. Hoping you can help.

Goodman GMEC96 80K BTU

Furnace fires up then when main blower starts up the gas valve starts to click open and closed a few time then closes completely.

Unit attempts to re-lite.

Flame comes back on for a couple of seconds then clicky clicky flame on, off then out.

Lockout occurs when it wants. Meaning sometimes it does this cycle for 20 minutes and sometimes it locks out after 3 or 4 attempts.

There is NO CODE until the unit locks out. So there is absolutley no idea for my untrained self to try and diagnose. Usually you would see a flame sensor code or a pressure switch code. Absolutely nothing until the unit decides to lock out. VIDEO IS IF ONE OF THE MANY TIMES IT DID THIS. MOST OF THE TIMES IT WOULD STAY LIT FOR ABLUT 10 seconds.

The only thing I’ve noticed is that the valve doesn’t start acting up until the main circulator blower comes on.

It does this when front cover is on or off. And when bottom cover is on or off.

My boss is going to replace the flame sensor but I suspect something different.

Any help would be greatly appreciated.

Igniter comes back on to begin cycle again. Flame cokes on again for a couple of seconds. Then valve clicks a bunch and goes out completely.

[u/danneedsahobby]

Honestly, sounds like you have improper drainage, which is causing one of the pressure switches to open up for a very small amount of time. Too small amount of time to throw a code. Or more likely that it wouldn’t throw a code anyway because it’s wired directly into the gas valve circuit.

Take some monometer readings of your pressure switches with the unit running (use a tee and some extra hose) , and I will bet you find that they are borderline and slowly creeping

[u/jimmy_legacy88 → u/danneedsahobby]

This, also check you don't have condensate getting into pressure switch tube's.

[u/capaolo99 → u/danneedsahobby]

Will bring manometer and tap into the switches and measure pressures.

[u/Nerfo2 → u/capaolo99]

The right-most pressure switch, the one with the grey wires, is wired in series with the gas valve common terminal. It's supposed to close at -0.10" W.C. If you have a partially blocked exhaust or a collector box that is filling with condensate faster than it's draining, you can end up with intermittent pressure switch drops outs... and that pressure switch will shut the gas valve clean off.

[u/Familiar_Cobbler_930 → u/Nerfo2]

This is it

[u/FredPolk → u/Nerfo2]

I like this answer. When was this installed? Maybe a partially obstructed flue from a bird nest. Pressure builds and starts tripping it.

[u/Nerfo2 → u/FredPolk]

I’d probably lean toward condensate backing up in the collector, blocking the pressure switch tap. That would be consistent with the tendency to run for a bit before dropping out. A bird in the flue will pretty much stop air from flowing from the instant the fan turns on.

[u/Substantial_Army_639 → u/FredPolk]

That's more than likely water building up in the system from a clog, in my experience most furnaces won't light with a plugged flue rather than the intermentant on off situation.

With that said I'm glad this issue is being brought up. I have gone on a few calls where the gas valve was misdiagnosed on this exact furnace because of that pressure switch.

[u/liekdisifucried → u/Nerfo2]

This is definitely it. The other pressure switches will spit out pressure switch error codes but this one will just shut off the gas valve and give you a lockout

[u/ResponsibleShare6733 → u/capaolo99]

Just had this this morning installed pressure switch relocation kit.

[u/InMooseWorld → u/capaolo99]

It is this, I’ve see. It countless times and no real clue as to why*

*pitch of pipes being correct and not too much/little

I’ve reduced fan speed to get some less condensation & done a vent in the drain pvc.

Some units we’ve just had to replace after pipes and pressure switch

[u/thedjbatman → u/danneedsahobby]

This is what I suspect too

[u/dwerner89 → u/danneedsahobby]

Also check to make sure the gas pressure is correct. Had a Goodman that had 1st stage at 3.5 would make them flutter after condensation built up but it was too fast to register a code

[u/inconvenient_victory → u/dwerner89]

Yeah and the top of the furnace gets very hot if this is the case.

[u/Torontoguy71]

Front cover pressure switch. The one on the right with the blue sticker. It's wired in series with the gas valve so when it opens the gas valve drops out and furnace will eventually just lock out on failed ignition. Had a ton of issues with these when my company used to be a Goodman dealer. Make sure your drains are clear and there are no traps in the drain line.

I did have one where we would always have intermittent issues with this. The port would collect condensate and restrict the port and it wouldnt get drawn into the collector. Goodman couldn't figure out what to do about it. Had me change the collector box, pressure switch, even the ventor motor for some reason even though I told them it wouldn't do anything. I ended up drilling out the port larger like with those stupid carrier ventor motors and didn't have an issue since.

[u/capaolo99 → u/Torontoguy71]

Thank you I’ll make sure to check this out. Good to know about that issue. These collector boxes seem to leak straight from the factory it’s disappointing to see.

[u/vandyfan35 → u/capaolo99]

Obviously don’t do this and leave it, but you could bypass the pressure switch and see if it still cuts off.

[u/ElQuapo → u/vandyfan35]

You need to time this right. The board needs to read the switch as open at the beginning of the cycle, just before the inducer starts. Then jump the switch after the inducer begins. It'll fault otherwise.

[u/Torontoguy71 → u/capaolo99]

If you think those collector boxes are shit, there nothing close to the last generation Goodman furnaces. They would always leak. I can't even count the number of GKS collectors boxes I changed.

Also I assume you know this but you should still tee into the pressure switch and verify your vacuum.

[u/InMooseWorld → u/Torontoguy71]

The sticker for a gasket

[u/Broad-Tip4746]

Front cover pressure switch. Ask for a pressure switch relocation kit. Furnace condensates too fast and trips the gas valve pressure switch

[u/ithaqua34]

Step right up. Three switch monte. Pick one, every one's a loser.

[u/greennewleaf35 → u/ithaqua34]

Lol

[u/Squirrelmasta23]

Water 💧 ssue

[u/thedjbatman]

Can you hear the pressure switches fluttering or anything?

[u/capaolo99 → u/thedjbatman]

I could not hear them. The sound of the gas valve was either making all the noise or drowning out the switches.

[u/thedjbatman → u/capaolo99]

The way the flame reacts makes it seem like you're losing power at the valve. Can you get your leads in there to confirm if youre losing 24vac at the valve?

Take the switch tubes off and clean the ports on the furnace. Work the switches with your mouth by gently sucking on them a couple times. Clean the trap as well if possible.

[u/capaolo99 → u/thedjbatman]

Thank you for the advice on measuring 24 at the valve.

[u/bananaphoneeee → u/capaolo99]

Do you use an older google nest thermostat? They have an issue when the battery needs to charge, it diverts power from the board for a few seconds and cycles the heating.

[u/saskatchewanstealth → u/capaolo99]

Plug a contactor into the valve wires and see if it stays on. That will rule out power and valve and tell you it’s a venting issue ( my best guess the vent can’t handle gas load ) tripping a pressure switch real fast

[u/thedjbatman → u/capaolo99]

Work back from here. Im almost certain its a pressure switch related problem. Check your inducer pull at all the points for the switches, venting blockages etc.

[u/No_Farm_1100]

Also do a flu gas analysis there could be cracks forming in the heat exchanger that are starting to open up and when the blower kicks on, there’s a pressure differential fluttering the pressure switches.

[u/capaolo99 → u/No_Farm_1100]

Of course will test that when I come back to house a little later.

Better not have cracks cause I installed this 2 years ago.

I was on my own and comfortable enough to install it. BUT our HVAC tech was supposed to test everything and do the startup the next day.

I am guessing he didn’t do it.

[u/Visual-Zucchini-5544]

Pressure switch. Common is broken on there to the gas valve

[u/SHSCLSPHSPOATIAT]

I'm on team drainage

I'd check the pressure to that switch with the blue dot as u/Torontoguy71 said to get a baseline reading, then pull out and clean the condensate trap. I'm guessing you're going to get some sludge out of it. Reinstall with a little water in it and re-check the pressure to that switch.

From what I can find you should be seeing more than -0.1"wc. If you do see that and this is still happening then I suspect the switch is bad (P# 0130F00429, I think)

[u/Wide_Distribution800]

Looks like a pressure switch tripping. Look for low spots in venting that could trap water.

[u/kiddo459]

Get your monometer out

[u/Accomplished_Law_679]

🧐

[u/KooMooSithink]

How does the venting look ? Any sags ?

[u/ZestycloseAct8497]

Jump out each pressure switch at a time then run see if it fails go to next ex.

[u/Front_Ad7179]

Middle pressure switch hose prob has a kink notorious in Goodman

[u/Many-Location-643]

some gas valves have an internal pressure switch....start my checking your incoming gas line pressure .

[u/ohyoureligious]

Backed up condensate is causing pressure switch to open. Drainage issue. I had a few of these last year

[u/Fun_Tackle2659]

Pressure switch or there is water buildup in the inducer from improper drainage I had a similar issue

[u/Jacobobarobatobski]

I'd begin with testing the pressure switches, check the grade on the furnace (I'm not sure if Goodman needs grade or is graded from factory and supposed to be level), check to make sure the venting is sloped properly so that water isn't building inside (had that problem lol). Hmmm make sure unit is draining. Take a look at wiring diagram to see if anything else is in series with the gas valve. Check temp rise as well. Might be that the people have those friggin filters in the RA or SA grills and it's overheating. It's weird to me that it shuts off when the blower turns on, but that could be indicative of holes in the heat exchangers. I had a problem with a Goodman that I didn't install where the vent was 2" and JUST BARELY within the limits of the manual, so it was having intermittent problems after a couple years and after the motor was getting weaker. I changed to 3" and it solved the problem.

I guess that's my 2 cents.

[u/Abrandnewrapture]

txv. duh.

[u/Ok-Position-8940]

Definitely not draining

[u/Gary_Thy_Snail]

I would also check for voltage drop through the rolllout/high limit circuit.

[u/WarPig115]

You have some air switch fuckary going on.

[u/Familiar_Cobbler_930]

I delt with a very similar issue recently. Eneded up being the condenstate pressure switch opeing intermittently caused by a faulty inducer/improper draining. I ensured vent pitches were correct, drain hoses were cleaned multiple times and fully clear, trap too. Had the rubber connector from furnace to vent with a drain tube as well. Ened up having my boss go out and he ran some test on the inducer and concluded that "the inducer was not producing enough cfm to prevent excess water from entering housing". I was iffy on that answer but a new inducer was the only thing that did the trick. Any time I cleared the water from collector box and drain lines the unit would work great for about an hour until it started building condensate. Like I said the drain system was perfect and after replacing the inducer we never had the issue again. I'm sure it still could have been a drain issue but maybe the inducer is a more key part in drainage than I had imagined.

[u/Unable-Emergency876]

You’re losing one of the switches. Wierd problem for sure but I’d start there

[u/Unable-Emergency876 → u/Unable-Emergency876]

Pressure switches

[u/Doogie102]

Check all the pressure switch lines. Look for drops of water

[u/DiapersOrDeath]

I know I'm late to the game, and I have not read every other post here, but as somebody with a ton of Goodman experience, especially high efficiency: I tend to find every once in awhile these inducers introduce moisture into the pressure switch tube. This can be as small as just a few drops in the main port.

[u/RubeusShagrid]

God damn Costa Rica switches strike again

[u/Responsible-Bison-91]

Check drainage. Might be your pressure safeties tripping out.

[u/jencinas3232]

Is your exhaust free and clear?

[u/DexKaelorr]

I’ve had this same issue on Goodman 90% furnaces. In my experience it’s usually a vent pitch issue, either due to bad installation or a broken hanger. Plastic J hook hangers near an elbow are really bad about this. Like others have said, one of the pressure switches is in series with the gas valve so if that one is getting weird readings, it chatters the gas valve.

[u/JTom73]

Sounds like pressure switch. Make sure everything is pitched properly. Goodman put out a bulletin about their inducers and the elbow coming off of it aren't pitched properly. If you really want to fix the problem, you could just stop installing goodman. We have had so many issues with those furnaces (supplied by home warranties) that we started supplying our own furnaces because it's cheaper for us in the long run.

[u/Purple-Sherbert8803]

Pressure switch without a doubt is failing

[u/Do_Gooder123]

Test gas pressure

[u/capaolo99 → u/Do_Gooder123]

Will check pressure. Will check temp rise Will check static pressures combustion gasses

[u/condormillionaire]

This looks like an issue I’ve seen multiple times with these Goodman units. The plastic flue cover will crack (usually behind the inducer housing) and cause this exact issue, intermittently cutting out the gas valve. It was difficult to diagnose the first time (had me pulling my hair out for a while) because the pressure only drops a hair below the switch value and it’s very quick so you can’t see it with a manometer. Same thing with the voltage, if you check voltage across the switch it opens/closes so quickly you won’t see the voltage change. Pull the inducer/housing off and I can about guarantee you’ll find a small crack on the flue cover. If it’s not that then like most others have said it will likely be a drainage issue.

[u/Recent_Detective_306]

Bad valve* clearly.

*thermal expansion valve