Boiler Clicking But Won't Fire

What's happening?

When the boiler is called for heat it runs the fan, opens the gas valve and sparks an electrode at the burner. The clicking you hear is that spark. If the gas lights, the clicking stops and the boiler runs. If it does not, the boiler tries a few more times, then locks out with a red light or a fault code and waits for a reset. So clicking without a flame means either no gas is reaching the burner, the spark is too weak or in the wrong place, the gas valve is not opening, or the boiler cannot prove it is safe to light, because the fan or flue is blocked. The fault code for this stage differs by make, so look it up in the manual.

What usually causes it?

• No gas reaching the boiler: a closed gas tap, an empty prepayment meter or a supply fault
• A dirty, worn or misaligned ignition electrode, or a damaged ignition lead
• A gas valve or its coil that is not opening
• A weak flame sensing rod that cannot confirm the flame
• A blocked condensate pipe or flue that stops the safety switches closing
• A failed fan or air pressure switch, so the boiler never reaches the lighting stage
• A circuit board that no longer sequences the start

Is it dangerous?

Medium. Unburnt gas can collect briefly when a boiler sparks without lighting, which is why it limits its own attempts. Do not override that. If you smell gas, leave the property, open doors on the way out and call the National Gas Emergency Service on 0800 111 999 (0800 002 001 in Northern Ireland). A boiler that keeps locking out should stay off.

Can I fix it myself?

Check that the gas tap at the boiler is open and that the hob works, which shows gas is reaching the house. On a prepayment meter, check the credit. Check the condensate pipe is not frozen in cold weather. Then reset once using the button in the manual. Do not reset more than twice and do not open the casing: electrodes, gas valves and fans are all gas work.

When should you call a heating engineer?

Call a Gas Safe registered engineer if the boiler still clicks without lighting after one reset, if it locks out again, or if it has shown the same code more than once. The engineer needs the exact code and when it appears.

What will the heating engineer actually do?

• Read the fault history and watch a full start sequence
• Check gas inlet pressure and working pressure at the boiler
• Inspect, clean or replace the ignition electrode and lead
• Test the gas valve, flame sensor, fan and pressure switch
• Clear and test the condensate trap and check the flue
• Leave the boiler lighting first time through a full heating and hot water call

Who fixes this

• Boiler repair

Questions people ask

Sources & References

1. Vaillant: boiler not igniting, common issues and how to fix them
2. Vaillant: how to reset a boiler
3. HSE: domestic gas safety, homeowner FAQs
4. Gas Safety (Installation and Use) Regulations 1998