Why won't my pilot light stay lit on my boiler?

Asked By: Salmane Mariner | Last Updated: 10th April, 2020
Category: home and garden home appliances
4.1/5 (137 Views . 30 Votes)
When the thermocouple is faulty, the gas valve can no longer stay open, which cuts off the fuel supply to the pilot light, causing it to smother out. If the thermocouple is extremely dirty at the tip, bent away from the flame or damaged, it could be the diagnosis of why the boiler isn't working.

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Keeping this in view, how do you clean a thermocouple on a boiler?

Use a screwdriver to loosen the screws and remove the thermocouple from the pilot assembly for cleaning. Use a piece of steel wool or the abrasive side of a sponge to gently remove the soot without damaging thermocouple. Avoid using cleaning products, especially those containing flammable chemicals.

Additionally, how do you know if you have a bad thermocouple? If you can't get the flame to light at all, and you're sure the gas is on, there's probably an obstruction in the pilot tube. If the flame lights and goes out when you release the gas control knob after holding it in for the recommended 20 to 30 seconds, that's the sign of a thermocouple malfunction.

Also Know, how do you change a thermocouple on a boiler?

Replacing a Thermocouple

  1. Shut off the gas and electrical power to the furnace.
  2. Remove the furnace's access cover.
  3. If the furnace has been running, wait 30 minutes for the thermocouple to cool completely.
  4. Unscrew the nut that holds the thermocouple end fitting into the gas control valve, using an open-end wrench.

Why is my boiler not igniting?

Burner won't ignite: This is the most common cause of a boiler failing to provide heat. If the gas jets on the burner will not ignite, no heat will warm up the water in the tank. The trouble may be due to a failed electronic igniter/pilot light, or perhaps trouble in the gas line.

27 Related Question Answers Found

Can a thermocouple be cleaned?

If the Thermocouple is faulty it will cause the unit to shut down. How to clean? Remove Thermocouple from pilot assembly, using steel wool or emery cloth to lightly clean the tip removing any soot or build up that might have accorded due to an improper pilot flame.

How do I know if my thermocouple is working?

Select the ohms or resistance option on your multimeter. Place one test lead on the side of the thermocouple and the other to the end that screws into the gas valve. If the thermocouple has proper continuity, a small resistance reading should be visible on the multimeter.

How do you fix a bad thermocouple?

A burned out or broken thermocouple should be replaced. To replace a thermocouple: Step 1: Unscrew the copper lead and the connection nut inside the threaded connection to the gas line. Step 2: Under the mounting bracket at the thermocouple tube, unscrew the bracket nut that holds the tube in place.

What causes a thermocouple to fail?

Changes in temperature can cause regular expansion and contraction in metal, which will cause thermocouples to weaken over time. After enough time, metal fatigue can cause a thermocouple to break.

Are boiler thermocouples universal?


Universal Gas Thermocouple includes universal adapter fittings and is compatible with screw-in, push-in or clamp-type pilot burners. It is designed for gas furnaces and 30 mV systems. The element is built for reliability and long life.

Can you jump out a thermocouple?

Harley said: Bypassing the thermocouple would make it no more dangerous than any propane grill. It's not going to make it explode. The only thing it would prevent is losing a tank of propane into the atmosphere if the flame happened to go out because the valve wouldnt close.

How do you troubleshoot a boiler?

No Heat or Poor Heat
  1. Thermostat – The first thing to check when boiler troubleshooting is the thermostat setting.
  2. Fuse box or circuit panel – Check the fuse box or circuit panel for a blown fuse or tripped breaker.
  3. Standing pilot – If the boiler uses a standing pilot light, check to make sure it's on.

How do I fix the pressure on my boiler?

How do I re-pressurise my boiler?
  1. Switch off your boiler and allow it to cool completely.
  2. Find the filling loop and check that both ends are securely attached.
  3. Open both valves to allow cold water to enter the system, keeping an eye on the pressure gauge.
  4. Close both valves when the pressure gauge reaches 1.5 bar.

How do you reset the pilot light?

Turn the valve to “Pilot.” Near the valve, you'll see a small button labeled “Reset.” Press this button while applying your lit match or butane fireplace lighter to the pilot light valve. Hold the flame steady until the pilot ignites, then release the button.

Is it dangerous if the pilot light goes out?


Can a Pilot Light Outage Be Dangerous? The worry here is that when a pilot goes out, the gas valve that supplies the fuel for the pilot flame could still be pumping gas. This can mean a buildup of gas, and when the pilot is relit or relights itself it could result in a very serious explosion.

Why do I have to reset my boiler?

Some of the most common boiler faults which could be triggering the need to reset it frequently include: A leak in the heating system. A blocked plate heat exchanger. An electrical part is faulty and needs replacing.

How do I reset my Vaillant boiler?

To reset the boiler manually, press the reset button (3) and hold for one second. If you are unable to resolve the ignition problem yourself by resetting the boiler three times, then consult your approved competent person.

How much does it cost to replace a thermocouple on a boiler?

Thermocouple Replacement - $20-$150
Calling a professional plumber to install a new thermocouple should only be up to $150. If you do the work yourself, you will only pay the price of the part which is about $20.

What does thermocouple look like?

The thermocouple looks like a piece of metal tubing smaller than a soda straw. To find it, first locate the gas control box. This is the box that the main gas line enters, where you turn the gas on in the furnace. The other end of the thermocouple sits in the flame of the pilot light.

Are thermocouples universal?


Universal Thermocouples. Universal thermocouples, as the name implies work on most water heaters. They are available online and in home supply stores for a reasonable cost. The length and the thread type are the two concerns when purchasing one.

Why does my pilot light go out when I release the pilot light knob?

The most likely of those is that the thermocouple needs to be replaced. The button you press to light the pilot bypasses the thermocouple. When you release the button, the thermocouple ensures that unburned gas doesn't get released by shutting off the gas when it's not heated by the burning pilot light.

How do you adjust a thermocouple?

To adjust the thermocouple, you must tighten the thermocouple nut with a wrench. Take care not to apply too much pressure to the nut -- just tighten it slightly. Then try lighting the pilot. If the pilot won't stay lit, replace the thermocouple with a new one of the same type.