What is the proper way to check gas valve with a multimeter?

genek79

Hello Everyone,

My Goodman GMT140-5D furnace will intermittently not ignite. What I mean is that the after the heat call from the t-stat, the inducer motor will come on, HSI igniter will glow for 15 seconds, but the burners will not ignite with flame. After 15 seconds and no flame, the igniter will shut off and try again, to the same result. This will continue until furnace locks out and will flash 1 continuous blink, which indicates an ignition failure fault code according to Goodman error code diagram.

This doesn't happen every time, but once every 1-2 days. It seems to mostly happen if the temperature inside the home was higher than the t-stat setting for most of the day (days are warmer in Colorado now, nights are still cold) and the furnace was not calling for heat for most of the day.

If I remove the rubber hose from the pressure switch, and blow in and out of the pressure switch, it will click, so I'm pretty sure it opens ok since I hear those clicks every time.

I've already replaced the igniter (twice), 120V/24V transformer, and the control board. I also had a an HVAC tech bend the HSI igniter bracket a little since he was sure that the igniter was too far from the gas burner and not sensing the HSI glow. That worked for a couple of days, but then the problem reappeared. I also already cleaned the flame sensor rod.

I'm thinking that the problem is either a bad gas valve or wiring (possibly from a bad grounding). I haven't replaced the gas valve yet. I'm thinking if I test the gas valve and it receives 24V when igniter glows, but doesn't open, then the problem is the gas valve. If I don't get 24V to the gas valve when the igniter glows, then the problem is the wiring/control board/ground, correct??

Can anyone tell me the proper way to check gas valve voltage? I'm thinking I should be checking continuity (ohms) by touching the gas valve terminals with the multimeter test leads (red test lead to red terminal, black lead to blue terminal) and the multimeter set the Ohms. If that's the proper way, anything higher than OL is good, correct? Or, is it better to check with multimeter set to AC voltage? Or should I remove the wires from the gas valve terminals and check with AC voltage? Again, I'm trying to see if the gas valve is actually receiving 24V from the control board...

Any other suggestions, ideas are greatly welcome...

Paul S_3

Meter set to ac voltage across the two terminals with the wires connected to gas valve....gas valve can be the culprit....but there can be other issues...pressure switch....are you sure you have gas there ....inlet and manifold pressure? Are the burners dirty?try taking them out and cleaning them...might be Better to have a professional come out

Eric_32

If your pressure switch didn't close/ pull in, the ignitor would never glow, it wouldn't get to that point.

The gas valve won't get voltage when the ignitor begins to glow will take a few seconds afterwards maybe 5 ish?

Read what voltage the gas valve operates at which will on a tag on the gas valve. most likely 24 volts but could be 120 volts.

Set your DMM to the next voltage scale higher than 24, on my UEI it's 40 Volts (AC). IF you do get voltage then I would be testing for gas pressure before the gas valve and the manifold pressure when the gas valve has voltage.

The ignitor will be 120 volts the gas valve is most likely 24, see if your transformer shows voltage on the secondary terminals. (24 volts side)

Jamie Hall

Be sure when checking that you are checking the voltage directly across the gas valve itself. They draw enough current that a poor connection (ground or otherwise) may cause them to fail to operate, even though the apparent voltage is high enough...

rick in Alaska

Long shot, but....... is the gas still turned on to the house???
Rick

ali6669

Hey so I have the exact same problem right now and it's 40 degrees, no heat on a Sunday evening. We got it running about 10 times and it lasts anywhere from 1 hour to 24 then quits again. I was wondering if you could tell me what your problem ended up being and what you had to relplace or repair. I refuse to pay another hvac guy to get it running for an hour then start guessing what the problem might be and attempt to get us to pay for random parts that may or may not fix it! Thank you...I sure hope u get a notification somewhere as I'm sure you don't watch this forum regularly.

Zman

@ali6669
It would be better to start a new post with all the details of your problem. Include the symptoms, model numbers and any error codes or flashing lights you may be seeing.

This post was from a "one hit wonder" never even bothered to answer a few questions....

shamie

I don't know if your problem was ever resolved n i realize it's two years later but i couldn't resist cuz i just went through very similar situation yesterday. My issue was resolved by replacing the meter itself. It was a gas pressure problem. It caused my heater to turn off along with hot water heater and stove n oven pilots wouldn't stay lit. It was clogged up in the meter n not allowing gas to flow through.