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Is Your Hot Water Cylinder Pilot Light No Longer Working?

Did your gas water heater suddenly stop working? Chances are the pilot light, which ignites the gas burner on your hot water heater, has gone out. If it has, you can try re-igniting it according to your water heater label. If the pilot light keeps going out, there are a number of potential problems to check.


  1. A bad thermocouple

The thermocouple allows gas to flow to the burner when it senses heat from the pilot. If it detects an unlit pilot, it automatically turns off the gas as a safety precaution. The thermocouple may stop operating if it is dirty, bent or damaged.

Rheem UV6379L 18 Inch Thermocouple Kit Water Heater Replacement

Dirt and grime can be cleaned off using a piece of sandpaper. If the thermocouple is bent far away from the pilot, you can simply bend it back to its original position, making sure it is close enough to the flame. The pilot light should appear blue in colour. If there is no clear sign of dirt accumulation or bending, then the device may simply be broken and needs replacing. This can be checked using a multimeter which tests the voltage coming from the device.

In theory, replacing a bad thermocouple is easy and only takes a few steps:

  1. Turn off the gas valve – do a quarter turn such that the handle is at a right angle to the pipe.
  2. Unscrew the nuts on the gas, thermocouple and pilot lines.
  3. Turn off the shutoff valve
  4. Remove the gas control and pilot light burner assembly
  5. Use a flat blade screwdriver to pry the spring clip on the thermocouple head and pull out the old thermocouple from the bracket.
  6. Install the new thermocouple (this should be the same type, size and length).
  7. Slide the burner assembly back in and reattach all three lines to the control valve.
  8. Relight the pilot, following the instructions carefully
  9. Reset gas control and refit access cover.


It is important to test for gas leaks, especially when replacing a thermocouple. When the gas burner turns on, soak a sponge in a 50-50 water/dish soap solution and wet the screw joints – air bubbles will indicate a leak.

A word of caution: before cleaning or cleaning, make sure to turn off the gas and wait for the thermocouple to cool to the touch. There will be a faint gas smell when you remove the gas lines, but this should dissipate within seconds. If the smell lingers, you should call your gas utility.

Working with gas carries a lot of safety risks, which is why we don’t recommend doing this operation yourself. It’s always best to err on the side of caution. Also, some hot water heaters also have a closed burner chamber that is difficult access, so it’s better to just call in a registered gas fitter.

Another thing is that, in some older models, the thermocouple can’t be replaced due to the unavailability or discontinuation of spare parts. Here at Hot Water Cylinders, we replace thermocouple on any brand, with the exception of Rheem.

  1. Flex tube problems

If the thermocouple checks out, you might want to check for flex tube issues. Sometimes, this tubing gets kinked in places, which disrupts the gas flow and prevents proper pilot operation. Unkinking may resolve the issue. But if it fails, you’ll likely need a new flex tube.

  1. Dirty pilot tube

If the thermocouple isn’t to blame, try checking the pilot tube. There might be dirt and grime buildup that obstructs the flow of gas. Unlike a broken thermocouple, a filthy pilot tube is much simpler to fix.

To start the process, turn off the gas and wait for the pilot to cool. Then, take a needle and clean the tube making sure to take out any blockage. After cleaning, turn the heater on and check if the pilot light will ignite. If it doesn’t repeat the process until everything works fine again.

  1. Main control valve issues

When all other issues are ruled out, the last thing you could check is the main control valve. It is rare for main control valves to go out but it is still possible. If you get a good result after testing the thermocouple using a multimeter, then a bad main control valve might be the culprit.

  1. Gas regulator issues

The gas regulator basically works by opening to let higher-pressure gas into the system and quickly shutting down when the “downstream” pressure reaches the desired level. The moving parts in this device are constantly in use and, hence, are prone to wear and tear. If the gas regulator is worn out, you’ll notice the pilot on your water heater, furnace and other gas appliances snuffing.

Other possibilities include a leak that is causing the burner to extinguish, an ignition that needs replacing or intermittent low gas pressure due to system fluctuations.

It’s a tall list of things to remember for the uninitiated, but a licensed gas fitter will have the expertise to find and fix the issue quickly and safely. They will also keep you from making errors that might make your warranty void.

If you are not able to light the pilot on your water heater, contact us on 0800 429 546 or use our advisor.