Have an old gravity furnace. Pilot generator putting out 575 mv, however gas valve won't open (ITT General Controls B60 gas valve).

How do I troubleshoot valve? What external or internal checks? I have the valve head off and looking under the diaphragm I don't see anything obvious.

I'm not sure how it works... when the 575 mv is applied it opens the small vent tube to relieve pressure on the back of the diaphragm?? The incoming gas pressure can then lift the very light spring pressure holding the diaphragm down? What should I be looking for?

Thanks!

Derek

Very old system. If the valve requires 750 Mv you might be a little short of the required voltage to open the valve. The pilot generator (power pile) might have to be replaced. All the parts are still available. Check Ebay for replacement.

I agree with hvac1000 the Mv are a little short. You can get a thermalpile at any hvac supplier.

I read another post from someone who claimed to have a spec sheet for the B60 valve; the poster said the valve only required 250mv to operate. My B60 valve works fine, and I have consistently measured the voltage at around 400 mv. A full 750 mv might in fact be undesireable; some voltage drop is generally anticipated by the resistance along the control wire up to your thermostat or other safety control. Those valves will fail at some point, obviously. But mine is 70 years old, and still amazingly reliable. It does get "stuck" once or twice a year, usually just after a major change in the weather. I very much would like a recommendation for a replacement part, just to have a spare.