Furnace pilot light problem

[drago52]

I have a Rheem RGDA-075A-AR furnace. Runs on natural gas, uses a bimetal thermocouple. It's about 30 years old. I can light the pilot light, and it stays lit. Upon a call for heat, the burners fire up and the fan enables and heats the house. Occasionally, when the heat call ends and the fan/burners turn off, the pilot light goes out. Occasionally, the pilot light goes out without any input from the Thermostat. I have cleaned out everything and replaced the thermocouple. Any suggestions on other places to look?

I can't find any manuals on the gas valve or the furnace (probably because it's so old).

[Canuck]

The pilot blows out when the main burners shut down, or after the burners shut down and the blower is in the cool down stage?

[drago52]

I cycled the system on/off several times in a row and the pilot light stayed on. 1 cycle meaning:
1- pilot light on, burners off, fan off
2- pilot light on, burners on, fan off
3- pilot light on, burners on, fan on
4- pilot light on, burners off, fan on
5- pilot light on, burners off, fan off

I did this three times just by calling for heat from the thermostat. The pilot light never went off. Because of this, I can't tell exactly when the pilot light fails. I can nearly guarantee that later this evening I'll go down and check out the furnace and the pilot light will be off.

A video might be more helpful. Here are a couple 1 minute videos of the unit staging on and off:
http://youtu.be/GLMKLidW_nw
http://youtu.be/OIy3Jad6CvM

[Foolds]

Wonder if the Evac Motor isnt working or it has a bad sensor making the unit think its not getting rid of the bad carbon monoxide

[edj]

There is a cheap sensor that determines if gas should be cut because pilot is out. If that sensor fails then the pilot will go out anyways. I had a similar problem and just wiggling the wires that feed from the thermostat to the inside solved it.

[drago52]

I definitely appreciate any input you thoughts you guys have. I went ahead and ordered a new, improved gas valve (they were pretty cheap) because my suspicion is the problem lies there, so I'll install that when it comes in a few days. I'm not mechanically challenged, so lemme know your ideas and I'll pursue them. Thanks!

[bornwildnfree]

Unhook gas line from heater...leave gas running...try and light...oh wait, that's what you do when you don't like your house, never mind LOL.

[drago52]

There is a cheap sensor that determines if gas should be cut because pilot is out. If that sensor fails then the pilot will go out anyways. I had a similar problem and just wiggling the wires that feed from the thermostat to the inside solved it.

I believe you are referring to the thermocouple. Yes, it has been replaced.


Wonder if the Evac Motor isnt working or it has a bad sensor making the unit think its not getting rid of the bad carbon monoxideI don't believe this unit (built in 1983) has an evac motor. I believe it just runs the fan more to clear the CO.


Unhook gas line from heater...leave gas running...try and light...oh wait, that's what you do when you don't like your house, never mind LOL.not interested

[Canuck]

Sorry about the delay before my response.

It sounds like the pilot blows out too easily when the main burners shut down. This is caused (usually) by improper air/gas mixture. A trick, is to adjust the burner baffles slightly closed to reduce the amount of oxygen/air, (or another way to think about it is negative pressure). When the burners shut down, watch the pilot flame and make sure it doesn't almost blow out, by too much negative pressure (suction sound) across it. If it seems like that's what it does, then the baffle adjustment may help out. If not, gas pressure may need to be adjusted as well.

[Canuck]

After seeing your video, the pilot burner needs to be cleaned out too.