Updated: Jul 6
This article explains how the thermocouple, gas valve solenoid, and pilot flame work on a water heater. I will be discussing 10 problems that may occur that causes the pilot flame to go out along with the solution for each example.
The following steps indicate how to light the pilot on the water heater and explains the key components within the water heater that make it work. Lighting a pilot should be fairly simple.
1. Locate the large red/white knob on top of the water heater’s gas valve. Locate the temp dial on the front of the gas valve. Also locate the sparker button. The sparker button is connected to a wire that leads to the pilot assembly.
2. Turn the front dial to the "pilot lighting" or "vacation" temp setting.
3. If the red/white knob on the top is in the on position, turn it so that it lines up with the word “pilot”.
4. Press down on the knob.
5. Continue holding down on the knob and push in the sparker button up to three times.
6. Look below through the peep sight glass or opening to see if flame is lit. It should be blue if it is burning clean and may be yellow where the flame wraps around the thermocouple.
7. Look to see if the flame is enveloping the thermocouple rod.
8. After 30 to 60 seconds, release the red/white knob
9. Turn the red/white knob to the “On” position.
10. Adjust the front temperature setting dial to the desired water temperature.
View the pic above to see what a solenoid looks like. This solenoid is inside the gas valve. When the white/red knob is pressed down on the top of the gas valve, it is actually pushing in on the solenoid. If heat is applied to the thermocouple (this is a 30 millivolt thermocouple) by the flame, then the thermocouple will apply electrical current to the solenoid to hold the solenoid in position. This means that after you release pressure on the white/red knob, the solenoid will remain in the same position as long as there is enough electrical current from the thermocouple.
The solenoid will hold itself in position to allow fuel gas through the first chamber inside the gas valve. This is the safety device for the pilot assembly. If there is no flame, then there is no heat to the thermocouple. This will cause the solenoid to close off the gas flow. However, as long as there is heat on the thermocouple, because of the flame, the pilot solenoid will remain open to allow the gas to flow. Gas will not enter through the second chamber until the temperature of the water falls down below the temperature set on the dial. The dial on the front of the gas valve is attached to a rod that will apply pressure to open the second chamber of the gas valve when the water inside the water heater becomes lower in temperature. After the gas exits the second chamber, the gas travels through to the main burner where the pilot flame lights the main burner. The main burner will remain lit until the second chamber closes when the temperature set on the dial has been reached.
The sparker does not produce a spark
First press the pilot knob down and then press the spark button ignitor in order to light your pilot. If the spark ignitor does not produce a spark, keep in mind that there must be a full electrical circuit for a spark to occur. The ground bar on your sparker must be on or very close to the ground of the gas valve. The spark rod must be about 1/8” away from the ground or pilot head. If the gap is too large, the spark may not be able to jump across the gap, to the ground.
· Bad sparker, needs to be replaced
· Spark wire is worn and touching the ground
· Spark wire is worn and jumping to ground instead of at the pilot termination
· Edge of the sparker is not touching the ground of the gas valve or something is insulating it.
· Spark rod is insulated by black or gray carbon dust and needs to be cleaned with non-soaped steel wool.
· Spark rod too far away from the ground/pilot head, gap bigger than 1/8”
Gas Off or Low Inlet Pressure to Water Heater
Check to see that the manual gas valve handle is in the same direction as the gas flow. This is in the on/open position. Also check that the pilot knob on the gas valve is turned to the pilot position. This can be confirmed by pressing the knob down all the way. Another issue could be that the manual valve on the natural gas meter could be shut off too. Yet another issue could be that the propane tank is empty. This is checked by looking at the gauge to verify how much propane you actually have available.
The inlet gas pressure to a propane water heater should be between 10-13” water column.
The inlet gas pressure to a natural gas water heater should be between 5-8” water column.
Check the gas pressure while the system is off as well as while it is on to make sure that there isn’t too significant of a pressure drop. Measure the pressure at the drip T cap or via the pressure tap on the gas valve. After checking, make sure that no leaks are present.
Pilot Flame Too Small, Low Pilot Pressure
If the flame is too small and does not envelope the rod, the thermocouple cannot generate the correct amount of millivoltage to hold the solenoid in the open position.
· Low pilot gas pressure, needs adjustment
· Clogged pilot tube
· Kinked pilot tube.
· Pilot orifice corroded shut or other type of clog is present
Pilot Flame Termination Head Bent, Not Enveloping the Thermocouple
If the pilot tube termination head is bent, the flame will not be in position to envelope the thermocouple. In order to fix the issue with the pilot tube termination, do not try to bend it as it may break. Just replace it with a new one.
Thermocouple Position Is Wrong
It is important to use the appropriate pieces in order to hold the thermocouple in place. The thermocouple should be pushed fully into position and locked in place by the locking/holding mechanism
Thermocouple Rod is Dirty, Needs Cleaning
The carbon dust created by the flame will insulate the rod from the full heat generated. This carbon dust needs to be cleaned off the thermocouple. Clean this with non-soaped steel wool.
Bad 30mv Thermocouple
Test the thermocouple to see if it is providing the correct amount of millivolts.
If it needs to be replaced, they are inexpensive. To check for voltage, the inner wire and outer wire must both be accessible. The inner wire is at the end of the weld connection. This can be removed from the gas valve with an adjustable wrench. Locate the inner and outer wire. (Do not check for voltage while the gas valve main burner is on.) Set the multimeter to Volts-dc and place one probe on the weld connection on the end of the thermocouple wire and the other probe on the outer wire. Press the pilot button down and light the pilot. Make sure that there is at least 10 millivolts present. If low or no millivolts are present, this indicates a bad thermocouple. A good 30 millivolt thermocouple with a good flame can produce up to 30 millivolts. The actual amount of millivoltage is determined by the amount of heat generated on the thermocouple rod.
A thermocouple testing adapter could also be used. This allows for testing of a thermocouple while the pilot and gas valve are in full operation.
Bad Water Heater Thermal Limit and Testing
Some water heaters have a thermal limit safety sensor to protect against overheating in the combustion chamber. The thermal limit safety sensor breaks the wire connection between the gas valve and the thermocouple. A loose wire connection or bad thermal limit will cause problems. Check the connections to make sure that they are all tight. If a thermal limit gets too hot at the sensing location, it will open up the electrical circuit and the red button will pop out. This needs to be manually reset. Inspection needs to occur to see why it is tripping.
There is also a thermal fuse by the temperature rod. This is sensing if the water tank overheats. This sensor is not visible unless the gas valve is removed from the water heater. This thermal fuse is not resettable and needs to be replaced if it opens up. This thermal fuse should not open up, unless there is no water in your tank.
To test if a switch is closed, test the electrical resistance across the switch with a multimeter. Disconnect the wires from the switch. A resistance measurement of 0.0 Ohms should be read on the multimeter on a non-powered and closed thermal limit switch.
Wind Blowing the Pilot Flame Out
If wind is the cause of a blown out pilot flame, the exhaust pipe terminating through the building may be too large in diameter, the height is incorrect, or it is in the wrong location. This causes the wind from outside to travel through the exhaust pipe and causes the flame to blow around. In this case, the thermocouple is not getting hot enough in order to produce the correct amount of current to keep the solenoid valve open. As a result, the solenoid will close and the pilot flame will shut off.
Bad Water Heater Solenoid
The solenoid is located inside the gas valve and the thermocouple connects to the end of it. If everything else is working, the problem is likely that the pilot valve solenoid in the gas valve is not working properly. The solenoid is rarely replaced because it is hard to get your hands on the proper solenoid. In this case, replace the gas valve. Testing of a solenoid is difficult because each solenoid is properly energized by a different amount of millivoltage. If the multimeter is reading 10 or more millivolts from the thermocouple, and the solenoid is not energizing and allowing the pilot flame to remain when releasing the knob, the solenoid is likely the issue.
I hope this helps you understand why a water heater pilot may not light or stay lit! If you are looking for a video to better help understand this topic, check out our "Top 10 Gas Water Heater Pilot Light Problems! Won't Light, Won't Stay Lit!" video below!
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Published: 05/06/2021 Author: Craig Migliaccio
About the Author: Craig is the owner of AC Service Tech LLC and the Author of the book “Refrigerant Charging and Service Procedures for Air Conditioning”. Craig is a licensed Teacher of HVACR, Sheet Metal, and Building Maintenance in the State of New Jersey of the USA. He is also an HVACR Contracting Business owner of 16 years and holds an NJ HVACR Master License. Craig creates educational HVACR articles and videos which are posted at https://www.acservicetech.com & https://www.youtube.com/acservicetechchannel & https://www.facebook.com/acservicetech/