Pilot not staying lit when firing

Pete Novak

Gentlemen. Once again thanks for the help. This is a very useful site. Second, I need some help keeping the furnace working @ an apartment I own.

The problem revolves around the pilot, and it's inability to stay lit when the burner fires. The typical scenario is as follows:

The pilot will light and stay lit when going through the normal lighting procedure. The flame is blue, about 1&1/4in high. It hits the thermal couple towards the top and the TC appears to have normal wear (no black). When the furnace calls for heat, the gas valve opens properly, all tubes light and fire evenly. Everything looks good.

Eventually, one of the shut offs will kick in, (low water, pressure, or thermostat). The gas valve will shut off, and the pilot remains lit. However, at this time the TC looks very bright red, as opposed to just when the pilot is on. Now, one of the shut offs will close, and it will attempt to fire the furnace again. This is where the problem starts. It seems that the gas valve will flow an instantaneous "burst" of gas. The burners fully light, but just as they light, it seems that the valve shuts off the gas and the flame goes out (reverse propagation??). Then, in a few seconds, the burners light again, but this time very slowly, one tube at a time, and it still takes a few seconds for them to come up to full flame. During this time, the pilot is half the size of what it normally was. Now the problem occurs with that instantaneous "burst" of gas. Sometimes, it blows out the pilot. When this happens, there is still a two second delay before there is gas again at the burners. Gas will flow again at the burners, but the pilot is out, so it won't light. However the gas only comes out for a few more seconds until the thermocouple cools. (safetys work properly) My question -
Is this action normal? If not how is the best way to remedy it? I was able to fix it yesterday by lowering the gas pressure. By doing this, the instanteous "burst" wasn't as big so it didn't blow out the pilot. If this is normal operation, I'm assuming an adjustment (somewhere) will remedy the problem.

As a side note, I do not have a contractor's license, however, I am an experienced mechanic, which means I'm very safety conscious and I'm well aware of when I'm getting over my head. This means if you post a solution that is out of my grasp, I'm not afraid of calling up a contractor to complete the job.

Thanks again

Pete

Wayco Wayne

I would

check the gas pressure on the inlet of the valve and see if it is dropping when the gas valve turns on. I could be the regulator at the gas meter or the regulator in the gas valve. Also check the gas pressure on the outlet of the gas valve. My guess is you need a new gas valve. Is it the original gas valve specified for that appliance? Some gas valves are designed to come on slowly, others to come on all at once. It could be it was replaced with the wrong one once upon a time. WW

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frank s

what you have........

Is a problem, first off what type of furnace do you have , and what is the approximate age? Do you have a seperate pilot tube that comes off the gas line??? Not from the gas valve, tell me a little more and we'll help you a little more.
Frankie sev

Unknown

It sounds like a pessure problem

as Wayco Wayne told you the pressure needs to be checked.

You could also have a partially plugged sensing port on the outlet side of the gas valve. A pro should check that.

When this problem occurs is any other gas equipment affected?

Is the gas coming to your house high pressure or low pressure? What is your location? You can tell by going to the meter and if there is no pressure regulator at the meter it is low pressure. This time of year it is not unusual for low pressure gas to drop down below minimum inlet pressure for the gas valve. The minimum pressure for inlet should be 5" WC if it drops below this it will affect ignition. It is also important to know that pilot gas is not regulated it is on line pressure. If you have a pressure problem the pilot will be sucked out or the concussion from the flashback you are describing will cause it to happen.

What I suggest is to get the gas company to come out and check it. If your local gas company does not do service then call a contractor. Ask the contractor when you call if they are familiar with gas pressure problems and how to test.

Pete Novak

Utica boiler and white rodgers gas valve

Hey thanks for the responses. I'll answer all the questions in the morning, but for starters the system can be described as follows: The boiler is a Utica boiler, and as stated the gas valve is a WR 36C03. It's 24 volt w/ no ECO (energy cut off). The boiler (I didn't get the model#, but I'll get it next time) was new in '87, and the gas valve was new in '00. (based on the service record on side of boiler). I'm not sure if these pieces are matched for each othere, but since I lowered the pressure on the valve, the pilot has not gone out yet. I'll post more tomorrow.
Thanks - Pete