Goodman gas valve voltage is erratic

JE223 · February 20

I have only been in HVAC for 2 years, but I have a more experienced boss.
I am working on a Goodman single stage 96% furnace with AC.
The unit is only 1 ½ years old.
I am having issues with the flame going out. The only code is EE0 which means it is locked because of too many retries.
The furnace lights, after a few seconds the flame sputters, then burns steady. Just about the time the fan turns on the flame goes out. This only happens when the furnace is cold. If I let it run it will do this a few times and then it will work the rest of the day.
I have checked all of the usual suspects.
I have watched the flame closely when it goes out. It is not being blown out like a cracked heat exchanger would do.
No clogged drain. No clogged flue, filter is new.
Temp rise is 40F never exceeds 110F in duct.
Checked the flame sensor: 2.6 micro amps, replaced it anyway
Checked incoming gas pressure: 10 inches at idle, 6.5 inches at full flame. Natural gas.
Checked pressure switches both work and pressures are within spec. -1.35 flue and -.085 drain. Bypassed each to be sure.
Checked all over temp switches. All work. Bypassed each to be sure.
Checked wires and connectors.
Replaced circuit card.
I bypassed the entire circuit and connected the gas valve directly to the transformer and it runs flawlessly.
With everything connected correctly, I checked the voltage to the gas valve from the circuit card. It reads 26.5 volts when working, then it drops and comes right back up which causes the flame to sputter. A few seconds later when the fan comes on the voltage drops and the flame goes out.
I am stumped. Any help would be appreciated.

ratio · February 20

Sure sounds like a control board to me, although I'd give the harness a wiggle test & go through and remate all the connectors once or twice before I condemned the board. Do you hear/feel a relay clicking when it happens? Might watch the voltage right at the xfrmr for a while, too.

worldclasshvac · February 20

I've seen this scenario a few times and it was because of the venting. Too long/too many fittings. If you add up your fittings and pipe and you are anywhere near the 50ft mark I would start there if it's all in 2" pvc. The pressure switch can flutter and not completely kill the flame and nuisance trip. Otherwise if you are dropping voltage for sure replace the board under warranty. Some of their units have the 2 pressure switches that use the lower rated one as a gas valve safety. Its right in line w the incoming 24v feeding gas the valve and can flutter killing the flame. You tested both the PS but did you hook your mano to the inducer and check for what it's drawing while running? You can jump PS to verify the draw for a min or two of run time

EBEBRATT-Ed · February 20

Sounds like you are getting a voltage drop when the fan starts. Check wiring connections blower amp draw and check low voltage when blower fan starts.

also check 120 when fan starts. If it is dropping off low voltage will as well

JE223 · February 21

I have already replaced the board. It has the same problem. I have bypassed the entire circuit by connecting the transformer directly to the gas valve at the same time I connected the meter to the Brown wire that is supposed to power the gas valve. The flame is steady and the voltage on the brown wire fell and came back up at the usual times. The voltage problem is definitely in the brown wire. I ohmed the wire while wiggling and pulling on the wire no issue found. I opened the pin on the connector, so it would fit tighter. The vent piping is about 10 feet long total with two 45 deg elbows and two 90 deg elbows on top to face down. It is all 2". I did hook up the manometer with a t to watch it in real time. Pressures are steady and better than they need to be to hold the pressure switches closed(-1.35 flue and -.085 drain). I see that I didn't make that clear in my first post. I have watched the voltage at the transformer and it is rock steady so is the 120v supply. It makes sense that their could be a voltage drop causing the problem and it makes sense that it is coming from the card, but I can't find it. It is hard to believe I bought a card with the same problem.
Where can I have a 24v drain that is not on the card? Maybe I should disconnect the fan and see if the voltage still falls off to the the gas valve? I really appreciate your comments.

109A_5 · February 21

Hello @JE223,
Look at all the stuff the R side of the transformer has to go through before it gets to the Gas Valve. The C side has a lot less stuff. Your excessive Voltage drop seen on the Brown wire may be from any of these devices or maybe a few that add up. Also bad crimps, connections and circuit board solder joints should be considered. You could measure the Voltage drop across a single device or a group of them.

ratio · February 21

Hmmmmm. I do have a 90+ two stage that won't run on high fire. As near as I can figure, something about the intake &| flue would start to oscillate on high fire but not on low fire. The flames would start surging & lock out after a few minutes or so. This was a temp install for heat during construction, so the flue & intake were just slapped in (although meet the mfgr's specs). I got it to run by just pulling the intake off. Once the mech room is complete I'll scooch it to it's final location & rerun the piping.

I've also seen pressure switch issues with a compromised HX. Everything looked good & was within tolerances (pressure switch, etc.), combustion analyzer said things were great, but the unit wouldn't run until it was warmed up. Trane tech support condemned the HX. (It was someone else's warranty baby, so IDK what ended up happening with it.)

JE223 · February 22

I have bypassed the grey wire circuit by replacing it with a ground wire directly to the chassis. I think the only things I haven't bypassed are the roll out switches and the primary limit switch. I assumed that since the rollout switches are manual reset and have never tripped they are good and the primary limit switch ohms good, but it might have intermittent contacts. It sounds like you are saying a loose connection at any of these could cause voltage flutter?

JE223 · February 22

I actually started by increasing the intake to 3" because it seemed to go out when I attached the intake pipe. That was not it. It still happens with the front cover off. I have checked the pressure switches and completely taken them out of the circuit.
Voltage still fluctuates. I can't see how a bad heat exchanger would affect the voltage with the pressure switches out of the circuit. Cracked heat exchanger is still an option, but probably last on my list. It might be the problem, but at that point I will need to replace the furnace.

pedmec · February 22

What is the error code after you get the first failure? you need multiple fails before it goes into lockout so you should get the error on the board.
And where are you measuring you gas pressure. you need to measure your manifold gas pressure not just upstream of the gas valve
.

Jamie Hall · February 22

Let me be sure I have this straight. Right back up in your first post (I think) you noticed that it runs perfectly when applying voltage to the gas valve direct from the transformer (brave soul), bypassing the control board? But that when the control board is in the loop you get that voltage drop problem? Before you swap out the control board again, go over the wiring from the control board to the gas valve with a fine tooth comb. All the plugs and sockets -- clean and bright? Tight? Then look at the wiring. Tight to any socket pins? Wiggle vigorously -- any looseness is suspect. Then look along the wires. Any worn insulation? Missing insulation? Possible breaks? Possible shorts?

Then do the same thing for all the other wiring...

And if you know what to look for, check the board for cold solder joints at any plugs or terminals or plugin relays.

109A_5 · February 22

Hello @JE223,
So transformer 24 VAC is always stable.
Transformer connected directly to Gas Valve, the Voltage at the Gas Valve is then stable and the flame is stable.
The C wire side of the transformer to the Gas Valve path has been substituted with no change in erratic operation.

I would systematically with a meter or jumper wire (or both) test the R side of the transformer to the Gas Valve path, this path is all that is left, but it has the most items (as annotated in a previous post). Don't discount anything, idle contacts (that never move) may oxidize more than active ones. Divide and conquer, split the path in half, looking for the erratic Voltage. The pink wire is kind of in the middle and the end at the limit control or roll out switch may be easily accessible. If the Voltage is good there the problem is toward the Gas Valve. If it is erratic there the problem is toward the transformer.

Initially I would disturb as little as possible while testing, so the problem does not magically go away.

Common Multi-Meter type Ohmmeters test with a very low sampling current and may be deceiving, in some cases Voltage measurements with normal circuit currents can be much better.

I'd like to say I have seen it all, but I probably have not. Some examples;

Bad solder joints on control boards, very common at relay pins and the joints where the 9 or 12 pin connectors are etc.
Bad crimps where wires are terminated to connector pins, even crimps that look good and feel good.
Bad crimps or actually loose rivets that go through the plastic case (or the like) connecting the wiring connectors of switching, limit and/or control devices to the stuff inside the device housing.
Connector pin fitment (they don't mate snugly).
Wire conductors fractured under the insulation.
Rubbed through insulation causing intermittent grounding, so the Voltage appears to be dropping out.
Corrosion.

It's a Treasure Hunt.

JE223 · February 23

I went to work on the furnace today and there is no issue. Everything works fine. I don't think I mentioned this happens a lot. Part of the reason I can't fix it. Sometimes it works for weeks and then quits again.
There are no other error codes, just EE0. I have created some errors by bypassing items, but if I don't cause them, just EE0. I have not measured the manifold pressure. I will.

JE223 · February 23

Yes you have it right. I bypassed the control card and hooked up the gas valve to the transformer. I just did it in sequence while the furnace was starting. I did not put anyone at risk. This is one of my vacant rentals, so if I screw up it's all on me. Even with the gas valve bypassed, I can see the fluctuation in voltage, it just doesn't affect the flame. I have wiggled wires, cleaned the harness to look at it, ran my fingers up and down the wires, removed the card and looked for cracks with magnifying glasses, checked each pin and tightened them including all spade connectors.

JE223 · February 23

I didn't touch anything this week and the problem "magically go away."
I will start over with the static switches first, because I didn't really eliminate them I just ignored them.
I hope the problem reappears, so I can kill it.

ratio · February 23

I've had pressure switches that didn't snap open/closed properly, especially with pressures that bounced right around the setpoint. Symptom was squirrely voltages because the contacts were showing high & low resistance instead of open & closed. Pressures that went well above & below the setpoint quickly enough would result in the switch operating correctly.

109A_5 · February 23

Hello @JE223,

JE223 said:
Even with the gas valve bypassed, I can see the fluctuation in voltage, it just doesn't affect the flame.

There really should not be much fluctuation in the Voltage, except when the inducer and/or the blower motor starts an even that should be minimal. Do you see 24 VAC at the Gas Valve or is it low. If it is low and the all extra added resistance of all the stuff on the R side between the transformer and the Gas Valve may make the Gas valve Voltage lower (too low) and erratic. If the 24 VAC is fluctuating at the transformer, what is the 120 VAC side doing ?

JE223 · February 24

The problem came back. I checked it this morning and it had the EE0 code, but this time I have two more codes EE4 shorted flame sensor and EEE bad circuit card. As soon as I can I am going to take the entire harness out and check each wire. The 24v is sitting at 26.5v and the 120v is 120v.
I ordered a new primary limit switch and put it in this morning. It made no difference.

ratio · February 24

Have you checked the wire to the flame sensor?

pedmec · February 24

Remove the switch cover and make sure you are properly grounded. if you are not properly ground you will get nuisance trip outs. Had an electrician wire up a new carrier and for some stupid reason never grounded the power feed to the unit. It caused nuisance call backs. I connected the ground to the furnace body and switch and it took care of the problem. Might want to check back at the panel if that looks good.

109A_5 · February 25

Hello @JE223,
You started this thread with "gas valve voltage is erratic". Without solving that problem all sorts of bizarre behavior may be expected. Poor power quality to the micro-controller (control board) may drive it nuts. Apparently the erratic voltage is intermittent and you may have to catch it in the act, which may be time consuming.

Since you mentioned the erratic voltage was seen at the transformer's 24 VAC secondary, I can't help but wonder if the 'Actual' problem may not even be in the furnace, rather a power issue in the building or utility. For example if the neutral from the utility is failing it can cause voltage issues that can be intermittent. Does it act up more on a windy day ?

If it is a power quality issue to the furnace, simply replacing the furnace may not help.

JE223 · February 25

I have checked the ground and added another ground wire from the power cord directly to the factory ground location. I do not see the erratic voltage at the transformer. It is only on the brown feed wire from the circuit card. I did check the wire to the flame sensor, but just with ohm meter and visual where it is accessible.

ratio · February 25

Do you have a megger or insulation tester? Those can be used to find certain wiring faults, like a weak spot in the insulation that occasionally shorts out due to e.g. thermal expansion. They're basically ohmmeters that use a high voltage (up to 1000V with my Fluke, but industrial meters can go well into the kV range) to find high-resistance (2.2 GΩ with said Fluke) shorts.

ratio · February 25

I forgot, did you say that you jumped the pressure switch out after the burner lit? That would be something I'd try if you haven't already, but you'd have to do it a few times when the problem is actually happening to prove it to be the cause.

pedmec · February 25

power cord? this is not hard wired?

Jamie Hall · February 25

pedmec said:
power cord? this is not hard wired?

That is a code violation right there. So -- to add to the merriment, get it hard wired and make sure that the boiler itself is bonded to your grounds at the switchboard.

JE223 · February 26

I don't have a megger. I did jump the pressure switch after it lit and I also replaced the pressure switch. Almost every residential unit I have worked on (not one I installed) has the air handler/furnace plugged in and the compressor hard wired. It never even occurred to me to check the code.

109A_5 · February 28

Hello @JE223,
@SuperTech just posted this in a similar thread, maybe it will help you.
https://forum.heatinghelp.com/discussion/comment/1793340#Comment_1793340

"I've had issues with Goodman/Amana/Daikin two stage furnaces doing what you described. The problem was condensate drainage from the flue pipe. They have had issues with a defect in the rubber 90⁰ elbow that connects to the inducer. Some of these elbows have a little rubber "lip" on the inside that prevents condensate from draining into the trap and causes excess condensate to drain into the secondary heat exchanger and it causes the pressure switch to chatter. The furnace won't show a fault code when this happens. "

JE223 · February 28

I will definitely check the rubber elbow. Thanks

JE223 · March 3

The rubber elbow did have the flashing issue. It was holding water and not allowing to drain. I removed the excess rubber. We will see if that was the problem. Thanks.

JE223 · March 8

It has been about a week since I modified the rubber elbow and the problem has not returned. Before I worked on the elbow, I could duplicate the issue very consistently by letting the heater cool down and starting it. I can't duplicate it anymore. I am very reluctant to call it fixed because it has eluded me for a full season, but I think it is fixed. The only thing I did before the problem went away was modify the elbow, so water can drain down the condensate line. I spent $300 on parts and probably 30 hrs working on this heater. 10 minutes with an Exacto blade and the problem goes away. There is no way I would have ever found that issue without everyone's help. THANK YOU!

Goodman gas valve voltage is erratic

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