6 Reasons Why a Water Heater Pilot Light Won't Stay Lit

A water heater next to a tool box.

A pilot light that won’t stay lit is more than frustrating. Not only does it prevent a furnace from operating properly, but an unlit pilot can also steal away the comforts of a hot morning shower. Unfortunately, there are a variety of reasons why pilot lights go out, all of which are dependent on a number of factors. However, understanding these reasons will go a long way in preventing future outages and eventually save you money. Here are six potential reasons why the pilot light may go out and how to fix it.

1. Obstructed Thermocouple

Most water heaters operate with a thermocouple. This device is central to the operation and can tell if the pilot light is on or off by an electrical current that is powered by the pilot’s heat. Whenever the thermocouple detects an unlit pilot, it turns off the gas as a safety precaution. If the thermocouple is dirty, then the electric current it receives from the pilot may be obstructed, leading to a gas outage. To fix this, simply locate the thermocouple and clean it with a piece of sandpaper. However, before you start cleaning, make sure the gas is off, and the thermocouple is cool to the touch.

2. Curved Thermocouple

Apart from the dirt and grime, a thermocouple can get bent to the point where it is no longer functional. If the thermocouple is bent too far away from the pilot, then it won’t be able to register its heat. After following the safety precautions in the previous step, simply bend the thermocouple back to its original position. Just make sure it is close enough to the flame of the pilot. Typically, the flame should lightly touch the thermocouple or be close enough to heat the device. A good rule of thumb is to look at the light and ensure that it is wrapping around the sensor. Furthermore, a healthy pilot light should appear blue in color.

3. Damaged Thermocouple

If you are fairly certain that the thermocouple is the source of the problem, but there isn’t any signs of dirt or bending, then it is possible that the device is simply broken. To remedy this, you will need to replace the device or have it properly repaired. Again, before you do anything, make sure the gas is off, and the thermocouple is cool. Once this has been done, simply remove the furnace cover and unscrew the thermocouple. Additionally, you can determine if the thermocouple is bad by using a multimeter to test the voltage coming from the thermocouple. Any reading below 20 MV indicates a bad thermocouple.

4. Filthy Pilot Tube

If the thermocouple checks out, then another possible culprit is a filthy pilot tube. Dirt and grime can build up and block proper flow of gas. Luckily, fixing this is an easy and straightforward process. After turning the gas off and waiting a few minutes for the pilot to cool, simple take a needle and clean out the tube. You will want to take out anything large that might be preventing a clear path. After a good cleaning, turn everything on and see if the pilot will light. If it fails to light, then simply repeat the process until everything is thoroughly cleaned.

5. Flex Tube Issues

Another possible reason why a pilot won’t stay lit has to do with the flex tubing. This tubing connects to the gas controller and will ensure a steady stream of gas. Sometimes, this tubing will get kinked in places which will prevent proper operation. If this is the problem, then unkinking the tube will occasionally resolve the issue. If this doesn’t work, than new tubing will need to be installed. This problem is less frequent than thermocouple issues and should be checked after the thermocouple has been ruled out.

6. Main Control Valve

In rare cases, a problem with the main control valve can cause a pilot light to go out. Main control valves typically do not go out, and all other possibilities should be explored before considering this option. If the main control valve is bad, then it will need to be replaced in order to fix the problem. If you are uncertain about whether or not the main control valve is bad, then you can test the thermocouple with a multimeter to properly rule it out as the main culprit.