Pilot Light Keeps Going Out: Top 10 Reasons

Introduction – Pilot Light On Furnace, Heater or Boiler Keeps Going Out

Furnace pilot light wont stay lit? Furnace pilot light goes out occasionally? A pilot light is a small, continuous flame which is used to ignite the main burner in a variety of appliances such as furnaces, water heaters, and ranges.

Pilot lights going out is a common issue that applies to a variety of appliances such as furnaces, water heaters, and ranges. There can be a number of reasons why a pilot light may go out, with the most common being bad or dirty thermocouples, or thermocouples not being high enough or in the right position.

Furnace technician diagnosing a pilot light that keeps going out

That’s why it’s important to know the top ten reasons why the pilot light goes out and how to test it.

How To Light The Pilot

To light the pilot light, press down the plunger connected to the solenoid for two minutes, allowing the thermocouple rod to heat up and send a small amount of electricity to the solenoid, keeping the plunger down.

The thermocouple rod is used to control the flow of gas to the pilot light. When the thermocouple rod is heated, it sends a small electric current (on the scale of millivolts) to the solenoid, which induces a magnetic field inside the solenoid and keeps the plunger down and allows gas to flow through the pilot tube. This electric current is necessary to keep the gas flowing and the pilot light lit. The current is maintained as long as the pilot stays on and heats up the thermocouple.

This allows gas to flow through the pilot tube and light the pilot light. As the heat dissipates, the electricity turn off and the plunger rises, shutting off the gas and securing the pilot light in the on position.

The problem is that sometimes the pilot shuts off! Diagnosing what goes wrong with the mechanism we described is the focus of this article.

Thermocouple Rod – What It Is And Why Its Important

The first thing in testing the pilot light is to check the thermocouple rod. This is the part that heats up and sends millivolts to the solenoid in order to keep the gas on. If there is no heat, the solenoid will come back up and shut off the gas.

To test it, a thermocouple tester should be used. This connects the inner wire of the thermocouple and gives a contact. Then, the alligator clamps should be placed on the clamps, and the thermocouple tested. It should start to stick and hold at around 2.5 millivolts.

Problem 1: Bad thermocouple rod

Based on the above, the first problem that can cause a pilot light to go out is a bad thermocouple rod. This can be tested out by using a thermocouple tester, which gives a contact for the inner wire of the thermocouple. The thermocouple needs to reach a certain amount of millivolts in order for the solenoid valve to stay open and allow the gas to get to the pilot tube. If the thermocouple rod is bad, it won’t reach the necessary amount of millivolts and the pilot light will go out.

Problem 2: Dirty thermocouple rod

The second issue is a dirty thermocouple rod. This occurs when there is a thick layer of carbon on the outside, which acts as an insulator and prevents the thermocouple from generating enough heat. To fix this problem, you can use unsoaked steel wool to clean the thermocouple rod.

Problem 3: Thermocouple rod in the wrong position

The third issue is the thermocouple rod may not be high enough or in the right position to be enveloped by the flame. This is usually caused by the brackets or tension bracket not holding the thermocouple in the correct position. To fix this issue, you can simply adjust the position of the thermocouple so that it is in the flame.

Problem 4: Loose connection at the gas valve

A loose connection at the gas valve can cause the pilot light to go out. This can be caused by a poor connection between the thermocouple and the solenoid, which will not allow the millivolts generated from the heat applied to the thermocouple to reach the solenoid. If the connection is too loose, the pilot light will not stay lit.

Problem 5: Bad solenoid

A bad solenoid can also cause the pilot light to go out. The solenoid requires 1.5 to 2.5 DC millivolts to remain open, and if the solenoid is not generating enough electricity, the pilot light will not stay lit.

Problem 6: Low gas pressure

Low gas pressure or low pilot filling pressure can also cause the pilot light to go out. If the flame is too small, it may not be touching the thermocouple rod and the pilot light will not stay lit. The pilot flame can be adjusted if the correct inlet gas pressure is coming in.

Problem 7: Obstruction in the pilot tube

A kinked or closed off pilot tube can also be the cause for the pilot light going out. If the tube is clogged or kinked, the pilot light will not stay lit. To fix this, the tube can be taken off and cleaned up or replaced.

Problem 8: Manual gas valve is in “off” position

The manual gas valve outside of the appliance can also be in the off position, preventing the pilot light from staying lit. The gas valve should be in the on position with the handle facing the gas pipe direction.

Problem 9: Bent pilot termination head

A bent or worked pilot termination head can also cause the pilot light to go out. If the head is bent over or overheated, the flame will not envelop the thermocouple rod, and the pilot light will not stay lit. In this case, the pilot head should be replaced.

Problem 10: Flame continuously being blown out

Finally, wind blowing at the pilot flame can cause the pilot light to go out. This is because the pilot flame does not have a continuous heat source on the thermocouple. This could be caused by the exhaust location or pressurization inside the building, among other reasons.

Staff Writer
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