Gas valve diagnostics

pdaugherty

I have 24 volts going to an 80% York furnace gas valve assembly, I hear the switch click but no gas comes out. I have 6" incoming gas pressure and 0" on the manifold side. Hot surface igniter is working as designed. When checking continuity when the valve has a call it seems to come and go during the short time that it is on but the 24 volts seems to stay constant. Is my valve body bad or the silinoid bad on the gas valve?

delta T

The 0" manifold pressure is when there is power to the gas valve correct? How old is the unit, and can you take a picture of the gas valve? Any time the gas valve is not open the manifold pressure will be 0. My money is that you have a bad gas valve. Doesn't really matter if it is in the diaphragm or the solenoid, there are no serviceable parts at all. You must replace the whole unit. If you have power to the valve and the manifold pressure is still 0 then I would say you have a bad valve.

Be very careful checking continuity with power on, it is easy to short stuff out, as unlike reading voltage, you create a closed circuit through the meter and you can inadvertently send current somewhere it shouldn't go.

pdaugherty

Thank you Delta T,
So yes, assuming 24 volts are going to the switch, it does every time I checked it with the wires disconnected and I hear it click when connected, and even got continuity beeps on my meter when connected, (even though you say I probably shouldn't do that, oops,) still reading 0" on manifold side. 15 year old unit. I will get the new gas valve. Thank you!!!!

pdaugherty

Ok here is a riddle for you. It's a 15 year old 80% York natural gas furnace.
I replaced the gas valve and still have the same situation. The inducer motors runs, the igniter glows, then 24 volts to the gas valve, there is resistance through the switch on the gas valve when energized, 6.2" of pressure on the incoming side and 0" on the manilfold side. When I was replacing the gas valve I made sure the manifold was not obstructed. Any clues why the gas will not pass through the valve?

GW

It can't be too many things:
You have another bad valve
Your new valve isn't a 24v valve
You don't have 24 volts
You don't have incoming gas
You installed new valve backwards

May be time for new valve #2

Tim McElwain

Numbers and make on valve removed and same on the new one installed. When was the last time this unit was working?

What is the make of the electronic control and have you checked to see how long the igniter stays on before it does a retry?

j a_2

Just asking, is it wired correctly.....it does happen.....

JUGHNE

You may have 24 VAC to the gas valve, but all gas valves have some form of on/off switch or knob.
Some of the electric switches are very small.
I know a real "duh" question, but have overlooked it myself on startup. Especially 2 stage valves.

Fred

JUGHNE said:

You may have 24 VAC to the gas valve, but all gas valves have some form of on/off switch or knob.
Some of the electric switches are very small.
I know a real "duh" question, but have overlooked it myself on startup. Especially 2 stage valves.

HA! I've overlooked that tiny, tiny switch too. What's with making them so small anyway?

JUGHNE

Fred and Rick, do you think he would tell us if that is the case?
It would be a real bummer if that were the case for both valves.

This is how I have accumulated some extra parts. At least being in the business one has the chance to sell an item later.

Fred

Jughne, I doubt it. I'd be a little hesitant but maybe.