thermocouple voltage


Old 03-13-04, 08:19 AM
CMil's Avatar
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thermocouple voltage

Back to the Williams radiant gs wall heater. Whatcan I expect to see for thermocouple output voltage at the control valve? This heater has no connection whatsoever to outside power - no batteries or wall power to the thermostat.
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Old 03-13-04, 08:44 AM
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I think what you have there is call a pilot generator or a millivolt thermopile. this is all the power. the pilot light makes the power to work the valve through the tstat. take out what you have there and get a new one. Its not a thermocouple.. You need a replacement generator for a 250 or 750 millivolt application. ED
Old 03-13-04, 01:31 PM
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Hi CMil

The info Ed provided you is very correct. There is one other type of Pilot Generator (PG) It is the 500 milivolt unit. Middle sized to the 250 and 750.

The point here is the voltage output is based on heat supplied. A new and properly heated PG will supply it's rated amount.

Less heat less output. Which is why the pilot flame must be all blue and completely surround the element. As well as heat only the tip only and do so so it glows cherry red in color.

Age also effects output. Like most other items, age will effect and deteriorate the PG. More age equals less output.

Number of parts, devices and length of wire, etc in the circuit also effects total draw on the current produced. Which is one reason why there are three sizes of PG's.

PG's are also used in pool and spa heaters. Thus the need for the 750 milivolt size. Fireplaces and most wall heaters (without or without thermostats) usually use the 750 sized PG.

Hope that helps some.
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