Thermopile millivolts?
 

I have a gas fireplace (fireplace xtrodinair) thats about 11 years old and it would not ignite today.The pilot was on. I cleaned the thermocouple and the thermopile. I reinstalled them and got the pilot back on but the gas valve once again would not open. I have been given two different millivoltages to look for on the thermopile 330 and 750. I checked mine and found it to be around 380 - 400 mv range. How should I be able to find out if its the robertshaw gas control or the thermopile that is giving me trouble?

Is the gas valve turned from the pilot position back to "on" again?
Do you have an on/off switch, remote or a thermostat to control the fireplace with?

Yes the gas is back to the on position...I have a remote thermostat that controls the unit. I have checked the remote and taken the remote function out of the system in order to try and get the unit to fire. I have also "shorted" the wires going to the thermostat control to simulate the on possition...none has resulted in any gas turning on.

did you try tapping on the gas valve may be stuck from setting.....just fixed one vanguard....its been working fine since...

Yes I have tried tapping ...with no luck, but thanks.

At your measured powerpile output/ with good connections to the gas valve/with thermostat lines jumpered at the gas valve/ with all gas cocks fully open & the gas valve "on"....if it isn't opening...
change the valve.

Is my 400 millivolts from the thermopile enough to open the valve or should it be higher? I've been told it should be closer to 700mv. Just wondering.

it dosen't hurt to have a few repair parts handi....while i want to agree with how....I think I would change out the thermopile 1st because if my old memory recalls i want to say millivolts should be closer to that 700 range,,,,but have to admit don't do alot of millivolts systems...rusty.... ben sr

Thermopiles are cheap & easy parts to change (as ben points) out where as fireplace gas valves can often be the most difficult to access.

If you are measuring a thermopile while it is connected to a robertshaw valve, if it measures 326 MV or higher while the thermostat circuit is open, the power pile is considered strong enough to open the valve.
Your output seemed to be 50MV above that threashold.

Were you measuring your powerpile output when it was connected to the gas valve or on it's own?
Was the thermostat was on or not?

How and I are probably going to have to agree to disagree on this but, if you are only getting around 400Mv from the power pile then I would replace it first. I have never had one in 35 years of heating systems work well at that low of a voltage. I woild first ensure the powerpile is fully enveloped in the pilot flame when testing it.

I have taken readings with the thermopile wired to the valve, unhooked from the valve, thermostat open and closeds and all my readings come back between 380 and 400 mv.

To Dan, The flame is centered on the thermopile and enveloping the top 1/3 of the thermopile.

At this point I am going to purchase a new thermopile and valve. The shop will take the valve back if not used. I will hook up the new thermopile to the old valve and see if it works , if not I will install the valve and hope one of these two items fix the problem.....if not I will be back on later this weekend.

Should be good. The key is to have the probe "IN" the flame. I have seen some that the flame was so low that the flame was barely touching the probe which will not generate enough power.

Let us know how it works out for you.

Hey Gary
This may clarify RobertShaw's recomendations on powerpile measurements on their gas valves.
Goggle
www.robertshawtstats.com/spaw2/.../ControlTips-MillivoltSystems.pd...