How many millivolts should a thermocouple read?
The normal millivolt output is 25 to 35 millivolts; on some, you may even get up to 35. The other part of this safety pilot system is the electromagnet (power unit).
Can a pilot flame be too far from the thermocouple?
The pilot flame must be big and hot enough to heat the thermocouple to the temperature it needs to generate enough voltage to signal the gas valve. Sometimes the problem is simply that the thermocouple probe is too far from the flame.
How can you tell if a thermocouple is working?
If the thermocouple is working, you should be able to measure 30 to 40 millivolts of voltage at the connection end of the tube when the pilot flame is on. You can test this yourself using a multimeter, but you may need a helper to keep the pilot flame burning while you do it.
What should be the millivolt output of a thermocouple?
If the flame is adjusted to a sharp flame, it will glow “cherry red” this will cause the tip to be welded and eventually the thermocouple will fail. The flame should be adjusted to a soft blue flame, not roaring or lifting. The normal millivolt output is 25 to 35 millivolts; on some, you may even get up to 35.
How is a thermocouple connected to a gas flame sensor?
Some gas fired heating equipment relies on an electronic ignition to ignite the flame. Those devices generally will not use a thermocouple. If a thermocouple is used you’ll see a small copper tube (or in some devices an electrical wire) connecting the flame sensor to the valve.
What happens to the thermocouple when the pilot light goes out?
The tip of the thermocouple is placed in the pilot flame, generating a voltage which operates the supply valve which feeds gas to the pilot. So long as the pilot flame remains lit, the thermocouple remains hot, and the pilot gas valve is held open. If the pilot light goes out, the thermocouple temperature falls,…
What should the millivolt range be on a thermocouple?
The thermocouple millivolt range should be above 25 millivolts. If so then it is good. If you test the thermocouple with the multimeter and you get a reading above 25, then you have another issue. Importantly, always make sure the tip of the thermocouple is directly in the pilot flame.
How big should the thermocouple be for a gas flame sensor?
To make necessary bends to route the thermocouple into position between the pilot-sensing end and its screw-in connection to the gas valve, use the bending template in the installation instructions. If you don’t have bending instructions, use a round object 2-3″ in diameter and keep bends gentle, avoiding crimping or squashing the tubing.
When to replace the thermocouple in a gas valve?
Finally, if the reading is less than 25 millivolts replace the thermocouple as most standing pilot gas valves need 25 or more millivolts to keep the pilot flame lit. The thermocouple millivolt range should be above 25 millivolts.
