How to test the gas valve on a gas furnace with an ohmmeter

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I will be checking various gas valves to see if you can check the continuity of the solenoid with an ohmmeter. Some gas valves cannot be checked with an ohmm…

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grayfurnaceman says:

Unfortunately the valve must be replaced as a whole. It is probably best as inside of the valve is quite delicate. Thanks for the question.
GFM

Jason Beaudoin says:

Hi GFM.  Thanks for the vid. Do you know if the coils in the newer valves can be replaced, or if the entire valve needs to be replaced? My valve (White Rodgers 36E98 202) is sticking and requires a tap with a mallet on the “tall” coil to turn on. It is getting 24VAC. This is a Carrier furnace (58PAV11113112) that is about 19 years old.

Gary Smith says:

You should mention not to test the thermocouple coil with a 9 volt ohm meter to burn out the coil

grayfurnaceman says:

That’s the goal! Thanks for the comment.
GFM

Rodney Fisk says:

Thanks for the vid. I am at the 8yr mark and this is the kind of intermediate to advanced stuff that will get me to improve. I do maintenance and have largely learned from YouTube and books. Nobody working around me (including my vendors) seems to know anything. They are part changers. I’ve stopped calling vendors, because they screw things up worse than the original problem. These videos are very much appreciated. I’ve learned something in just the last day from watching.

grayfurnaceman says:

It is probably a flame sense problem. check out this vid. Furnace won’t start. Check the flame rod.

tausif304 says:

Hi, on regular basis my furnace stars and it runs for around 30 seconds and than once pilot lamp turns red, gas release valve releases gas. Lately when I’m having problem in my furnace that gas release valve releases gas ad after 5 second it shuts off gas, it keep doing that for 3 times and after that furnace turns off than I have to keep trying it till it works, can you please tell me do I need to change gas release valve or there is something else wrong in furnace mother board and not in valv

grayfurnaceman says:

Well, the rectifier thing I found out at night with below zero temps and no available gas valve. Bypassed the rectifier to get the valve to work. Was unsuccessful but I learned something. Thanks for the support.
GFM

talyn875 says:

Great information, you really know your stuff. Enjoy the videos.

grayfurnaceman says:

Sometimes I assume more than I should. In most cases, we are looking for 24-28 volts AC. The voltage is transformed from usually 120V AC. On some units, specifically hanging unit heaters, the gas valve can be 120V AC. Thanks for the comment.
GFM

Hendrik Fink says:

it would be nice if you mentioned what voltage we are looking for DC 24?

C Gonzalez says:

can the valve be clean or fixed some how ? I have an old furnace the burners dont ignite always, we had a certified guy and replace the fan motor and now he says we need to replace the gas valve. Can I fix this my self I cant really afford paying another 300 dollars

grayfurnaceman says:

Then I would have to agree it is probably the valve. Good luck.
GFM

Jason Colclazier says:

There is a wall mount heater that’s been running fine. I’m sure it doesn’t use as much as the furnace. Gas flow seems fine.

grayfurnaceman says:

Do you have gas? Possible regulator problem at the gas meter. Check with gas supplier.
GFM

Jason Colclazier says:

I wasn’t humming, the valve was… lol

Jason Colclazier says:

The pilot stays lit. But when I bypass the thermostat to fire the furnace, I hear the click. But the pilot just doubles the size of the flame. The burners don’t ignite. I wiggled the stat wires and I made a hum sound. I’m thinking I have a sticky valve that just isn’t fully opening up? Its not been fired in about a year.

grayfurnaceman says:

If the valve is working ok and it is not objectionable its fine. Not all valves run on DC. Merry Christmas
GFM

Jason Colclazier says:

What’s going on if you do get humming from the valve?

grayfurnaceman says:

Yes you could. The amp meter must read in .01 increments. And remember on newer units the gas valve is only on for 4 to 7 seconds on a trial for ignition. So the sequence is inducer on to prove pressure switch>HSI warmup>gas valve for trial for ignition.
GFM

quimshtgclg says:

Could you use an amp meter ?

grayfurnaceman says:

The pilot solenoid would normally have a very low resistance.  Make sure the button on the thermocouple is clean and has been tightened. Do not over tighten. If the pilot light is covering the thermocouple 3/8 to 1/2 inch it should hold in. Check out “the pilot gas furnace” playlist for more info on how the pilot should work. If it still does not work, the gas valve will have to be replaced. Good luck and let me know what happens.
GFM

manjiri prabhune says:

I have 36C04 222 standing pilot valve. The pilot was not remaining lit. I changed thermocoupler 2-3 months ago. It started the same problem again. No The pilot has 20-30 mV dc circuit (thermocouple) and main valve has 24 V AC circuit. I checked my main gas valve solenoid resitance of 64 ohm. For pilot solenoid the resistance come 0.1-0.2 ohm. Considering such a low voltage, it seems logical to have very low resistance. What is typical resitance of pilot valve solenoid?

grayfurnaceman says:

Well, as Sherlock Holmes would say, after eliminating all else, the only answer, however improbable is the one that works. There have been times when I said the same thing and never did find out why. If you find out why, send a note.
GFM

R. T. says:

So unit works now.
But I still have no clue why I did not have those 24 volts to MV
It was staring to rain and getting dark –no time for more testing. I’ll try to figure this out on the next job :) :)

R. T. says:

I went today to that rooftop equipped with valve and control module. I measured the voltage to PV -24V, measured to MV (after pilot was on) no voltage .So –it is the module? Then I jumped PV to MV after the pilot was lit- nothing happened. That left me clueless .Install the new module (universal) –no main gas .Swap the valve (universal).Clean main and pilot burner. That took some time. Bingo! Works. Swap the old module back .Works as well.

grayfurnaceman says:

The one on the opposite side of the burner is to assure all burners light. If your ign control is a Johnson they seem to prove very fast. Honeywell is much slower. If you have 24 volts to the main gas solenoid valve and the valve does not open, the valve is toast.

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