testing thermopile or pilot generators

[tomie]

Hey appplianceman 18007260692, with your millivolt tester how do you test a

themopile or pilot generator for wall furnace?

baba

[ACtechGUY]

Your pilot flame should be a lovely shade of blue. If it is yellow in the least , there may not be enough heat to generate the 20 or so millivolts required to keep the pilot soloniod energized. If you do have a yellow flame , disconnect the pilot tube at the gas valve and blow it out with compressed air or something similar. This will clear an oxide that builds up on the pilot orifice.

To test a thermocouple.You need a Multi meter set to dc volts in the millivolt range. Unscrew thermocouple from gas valve.(This test requires the use of aligator test leads or 2 people , one to hold the leads and the other to light and hold the pilot button) One lead on the outer copper and the other on the silver tab on the end that screws into the valve. Thermocouple should be encased in the pilot flame. With a good flame (sorry not a match or aim-n-flame) you will see the voltage climb over 20- 30 seconds to max out around 30 mv. You need a minimum of 18-20mv to keep a gas valve pilot open.

If you have a thermopile (It will have wires) then you should expect to see something like 300 to 500 millivolts in a functional thermopile.

[tomie]

Thanks ac tech guy,  On the wall furnace I worked on the problem was that the

burner would not come on.  Checked the gas pressure, cleaned out tubing, checked t-stat.

Tapped on the gas control, tightened wire connections.  All to no avail.

Finally took off cover and found the hi limit stat had tripped.

baba

[applianceman18007260692]

I heat up the generator with a torch to see if it puts out 750,000 or close to it. I use an old millivolt meter. Most of the time they either put out nothing or about half that. If the pilot holds but the gas shuts down when the operator is jumped that is a good indication the generator is weak. Of course these cost way more than ordinary thermocouples because the energy produced from them is what operates the valve. As a result you only need a cheap wall stat that makes and breaks.