Eco Happy (Solar Expert)

Published March 9, 2024

Your boiler pilot light can fail due to damaged components, gas supply issues, and even draughts. The pilot light is a small flame that stays on continually inside the boiler; it acts as the ignition spark for your heating system. Even though you normally don’t see this light, you hope it doesn’t go out. If it does, your radiators turn chilly and hot water soon becomes scarce,

In this Eco Happy guide, we’ll take a closer look at this small but crucial element of the central heating system. Read on to understand the pilot light’s features, why it goes out, and how to relight it in an emergency and keep the flame burning safely.

Pilot Light Explained

The boiler pilot light provides a small, steady flame in the boiler’s combustion section. This flame is always on and ignites the main burner whenever heat is required.

Why is the pilot light lit continuously? The idea is that the boiler can respond to a call for heat without having to create an additional ignition. However, modern boilers have moved away from the permanent flame idea. Today, electrical ignition on demand is considered safer and more efficient.

Older boilers feature a manual pilot light, while the ignition mechanism in newer boilers is sometimes called an automatic pilot light.

Manual pilot light

Manual pilot light refers to a setup with a permanent visible flame. If your boiler’s gas control knob has three settings – ‘On’,Off’, and ‘Pilot’ – your pilot light is manual. To relight a manual pilot light, you must physically light a flame.

Automatic pilot light

The term ‘pilot light’ is often used to describe both the permanent flame and a device that produces a flame only when needed. Electronic ignition systems that use spark ignition or hot surface ignition are sometimes said to have an automatic pilot light (also called an ‘intermittent pilot light’). The gas control knob for automatic pilot lights has only two settings – ‘On’ and ‘Off’.

How To Check Your Pilot Light

When your boiler stops working unexpectedly, the pilot light is one of the first things you want to check. Before inspecting the light, it’s worth first confirming you have power, the boiler is switched on, and there is no issue with your gas supply. Also, check your thermostat isn’t on the blink.

Once you’ve done these basic troubleshooting checks and found nothing amiss, go ahead and open your boiler’s front cover panel. You will either see the pilot flame burning or not. If the flame is blue, your light is fine and not the cause of the boiler failing.

If the flame is yellow or orange, it usually points to a dirty pilot light or obstructed burner. In extreme cases, it could indicate a gas leak, so you should consult a registered Gas Safe engineer as a priority, especially if there is a strong smell of gas from the boiler.

We advise you to check your pilot light periodically to see that it is burning a friendly blue colour.

Why Does Your Pilot Light Go Out?

Let’s look at the main reasons your pilot light dies.

Faulty thermocouple

The thermocouple (also called a flame sensor) is a safety device that detects the heat from the pilot light and sends a signal to the gas valve. This signal keeps the valve open, allowing gas to flow to the pilot light and burner. If the thermocouple does not detect enough heat, it will close the valve and cut off the gas to the pilot light.

When the thermocouple is damaged or dirty, it fails to properly detect the heat of the pilot flame and triggers the gas regulator to close, extinguishing the pilot light.

A faulty thermocouple can also send a weak or erratic electric signal to the gas valve, causing it to operate unstably. An unstable valve may close at random, snuffing out the pilot light.

Faulty thermocouple fixes

A dirty thermocouple can be cleaned carefully with a soft cloth. If your boiler engineer diagnoses that the thermocouple is broken, it must be replaced. Thermocouples are cheap; the main cost will be the installation charge.

Faulty gas valve

The gas valve controls the flow of gas to the pilot light and the main burner. It comprises two parts:

  • Pilot valve – supplies a small amount of gas to the pilot light.
  • Main valve – supplies a large amount of gas to the main burner when heat is needed.

A faulty gas valve may extinguish your pilot light in two ways:

  1. If the gas valve doesn’t open wide enough, too little gas flows to the pilot light. As a result, the pilot flame is too weak and battles to stay lit or burns feebly and erratically.
  2. In rare cases, a damaged main valve leaks gas into the pilot light. The back pressure this creates pushes the pilot flame away from the thermocouple. As we’ve seen when the thermocouple doesn’t feel enough heat, it closes the valve and cuts off the gas to the pilot light.

Gas valve fixes

Checking and dealing with a problematic gas valve is a job for a Gas Safe registered engineer. Sometimes, the valve has loosened, so tightening it will solve the problem. If it is cracked or damaged, it will need to be replaced. A valve is quite a pricey component, so expect to pay a couple of hundred pounds, including installation.

Dirty pilot light

A build-up of dirt in the boiler pilot light will compromise its performance. The pilot light’s gas jet is small and can get blocked with dirt and soot. When the mouth of the pilot light is clogged by dirt, it won’t be able to hold a flame. A weak flame, which usually presents as yellow, can’t reach the thermocouple.

Fixes for a dirty pilot orifice

Cleaning the pilot light orifice usually does the trick. This should be done by a certified person who uses compressed air and special brushes. Regular maintenance will help avoid dirt buildup.

Strong draughts

If your pilot light tends to go out when it is especially windy or when doors and windows have been left open, it’s a telltale sign that your flame is vulnerable to draughts. This is most common in poorly insulated homes.

Fixes for draughts

  • Make sure the cover on your boiler is properly secured and not loose or damaged.
  • Draught-proof your home as best possible to cut out cold gusts. This will also combat heat loss in your home. Consider these simple draught-proofing steps:
    • Seal gaps around windows, doors, and any other openings where wind gusts may enter.
    • Use draught excluders (a rolled-up towel works) at the bottom of doors.
    • Fit keyhole and letterbox flaps.
  • If draughts continue to blow out your pilot light, you may need to look at the installation setup of your boiler, including the flue and vent systems. If the existing arrangement exposes your boiler to unwanted airflow, you should weigh the cost-benefits of changing the setup to achieve better insulation.

Low gas pressure

In some cases, low gas pressure orinsufficient gas supply can affect the pilot light. Pilot lights need a steady supply of gas to keep burning. If the gas pressure is too low, they may not get enough gas to stay lit. This can happen if there is a problem with the gas line.

This is not a very common scenario as the pilot light only needs a small amount of gas to keep burning. It operates on a low-pressure flow (as opposed to the main gas burner, which needs a high-pressure flow).

How To Relight A Manual Pilot Light

Here is our 12-step guide to relighting manual pilot lights.

  1. Ensure all gas appliances in the house are switched off.
  2. Turn the gas control knob to the ‘off’ position.
  3. Locate the gas supply valve and turn it off. You don’t want any gas flow while you’re working.
  4. Wait about 15 minutes to allow leftover gas in the pipes and gas fumes to dissipate.
  5. Remove the boiler cover panel to get to the pilot light.
  6. Turn the gas control knob to the ‘Pilot’ position.
  7. Press down the knob and hold. Depressing the gas control knob allows for a controlled gas flow to the boiler’s pilot light hole.
  8. Continue to hold down the knob and use a long-reach lighter or a match to ignite the pilot flame.
  9. Keep holding down the control knob for roughly 30 seconds to one minute as the pilot flame becomes a healthy blue. This allows time for the thermocouple to heat up so that the pilot light remains lit when you release the knob.
  10. Release the knob gradually. The pilot light should stay lit; if not, repeat the above steps.
  11. Once the pilot light is stable, you can close the cover panel securely.
  12. Turn the gas supply back on to restore gas to the boiler. Set the thermostat to call for heat and see that the boiler ignites properly. If everything is firing correctly, your house should start heating up nicely.

Note: The general rule for gas boilers is that the unit under the cover panel should only be worked on by a Gas Safe registered engineer. If the boiler is under warranty, you could void the warranty by working on the pilot light. Remember to practise safety first at all times.

How To Relight An Automatic Pilot Light

Relighting an automatic pilot light is a little different from a manual light. Here is the 10-step guide to relighting automatic pilot lights.

  1. Turn the boiler off at its electrical switch.
  2. Access the pilot light assembly by removing the boiler cover panel.
  3. Turn the gas control knob to the ‘off’ position.
  4. Allow 10 minutes for the gas residue to clear.
  5. Return the control knob to the ‘on’ position.
  6. Turn the electrical switch back on.
  7. Watch and listen for the automatic ignition sequence. You should hear a clicking sound as the ignition system fires. Depending on the boiler model you may see a pilot flame. Alternatively, the igniter will ignite the gas directly at the burner.
  8. Allow a few seconds to see that the flame is stable and the ignition has been successful.
  9. Close the cover panel securely.
  10. If the ignition fails, you should turn the gas control knob ‘off’ again.


How often should I inspect my boiler’s pilot light?

It’s a good idea to inspect your boiler’s pilot light regularly, especially before winter sets in. Look for signs of dirt buildup, corrosion, and a weak or discoloured (yellow-orange) flame.

Is there a way to prevent the pilot light from going out frequently?

Regular maintenance of your boiler can help prevent the pilot light from going out. An annual servicing by a qualified engineer should include inspecting and, if necessary, cleaning or replacing the pilot assembly, thermocouple, and gas valve. Also, ensure proper insulation around the boiler to keep draughts at bay.

Is it dangerous if my pilot light goes out?

If the pilot light goes out and the gas valve remains open, there is a risk of gas leakage. A pilot light malfunction can also cause incomplete combustion, potentially producing poisonous carbon monoxide (CO). That said, boilers have built-in safety features such as thermocouples and shut-offs to prevent dangers like explosions and carbon monoxide poisoning – the risk is relatively low.

Fatal accidents do happen, however, especially with older boilers where safety mechanisms break down. If your pilot light keeps going out and your flame is often yellow, you need to consult a certified engineer. If you smell gas or are aware of gas fumes, turn off your gas supply and call a Gas Safe engineer urgently. Find out more about detecting carbon monoxide.


Like all boiler parts, the boiler pilot light sometimes fails. While it is fairly simple to relight the flame, safety should always be your top priority when dealing with gas appliances. If you are unsure about the process, it’s best to call a registered engineer. A faulty pilot light is often due to damage to the intricate parts. Checking, repairing, or replacing these parts should always be handled by an engineer.

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