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Boiler Won't Ignite? Here's What To Check

If your boiler won't ignite, don't panic. Ignition problems can be caused by low boiler pressure, thermostat issues, frozen condensate pipes or faults within the ignition system. This guide explains the most common causes, the checks you can safely carry out yourself and when it's time to contact a Gas Safe engineer.
Keystone London heating engineer carrying out a boiler service

Why Won't My Boiler Ignite?

Different faults can prevent your boiler from lighting. Explore the most common causes below.

No Gas Supply

If your gas supply has been interrupted, your boiler won't be able to ignite. Check whether other gas appliances, such as your cooker, are working.

Low Boiler Pressure

Most boilers require adequate pressure to operate correctly. If the pressure falls below the recommended level, the boiler may fail to ignite.

Frozen Condensate Pipe

During cold weather, the condensate pipe can freeze and block the boiler's safety system, preventing ignition.

Ignition Component Failure

The ignition electrode or flame sensor may become worn or damaged over time, preventing the burner from lighting correctly.

Faulty Thermostat

If your thermostat isn't calling for heat, the boiler may appear not to ignite even though the appliance itself is functioning normally.

Electrical Supply Issue

A tripped fuse, power interruption or faulty electrical connection can stop your boiler from starting.

Why Are My Radiators Not Heating?

Radiator heating problems can have several different causes. Identifying the most likely issue will help you decide what to check next.

Air Trapped Inside

Air pockets stop hot water from filling the radiator evenly, leaving cold areas at the top.

Sludge Build-up

Over time, rust and debris can collect inside radiators, reducing heat output and restricting water circulation.

Low Boiler Pressure

Low pressure can prevent your heating system from circulating hot water effectively.

Faulty Thermostat

If the thermostat isn't calling for heat correctly, your radiators may remain cold even though the boiler is switched on.

Stuck Radiator Valve

Thermostatic radiator valves (TRVs) can seize after long periods without use, preventing hot water from entering the radiator.

Is It a Serious Problem?

Not every ignition problem requires an emergency repair. Use the guide below to understand how urgent your situation may be.

Usually Normal

Some ignition issues have simple causes that you can safely check yourself.

Common situations

  • Boiler recently reset
  • Low boiler pressure
  • Thermostat settings
  • Temporary power interruption

Action

Carry out the basic checks below before arranging a repair.

Needs Attention

Repeated ignition failures usually indicate a developing fault.

Common signs

  • Boiler clicks but won't ignite
  • Boiler repeatedly locks out
  • Fault code displayed
  • Boiler keeps needing to be reset

Action

Arrange an inspection if the problem continues.

Call an Engineer

Some ignition faults require immediate professional attention.

Warning signs

  • Smell of gas
  • Burning smell
  • Electrical burning sounds
  • Boiler leaking water

Action

Switch the boiler off and contact a Gas Safe engineer immediately.

6 Quick Checks You Can Do

Before booking an engineer, try these simple checks.

Check the Gas Supply

Check Boiler Pressure

Reset the Boiler

Check the Thermostat

Look for Fault Codes

When Should You Call an Engineer?

Contact a Gas Safe engineer if:

  • Your boiler repeatedly fails to ignite.
  • Resetting the boiler doesn't help.
  • You smell gas.
  • Your boiler displays recurring fault codes.
  • Your heating and hot water have stopped completely.
  • The boiler keeps locking out.

Ignoring repeated ignition faults can lead to complete boiler failure and more expensive repairs.

Can You Prevent Ignition Problems?

Annual Boiler Service

Routine servicing helps identify worn ignition components before they fail.

Maintain Correct Pressure

Keeping your boiler pressure within the recommended range helps ensure reliable operation.

Protect the Condensate Pipe

Insulating exposed condensate pipes helps reduce the risk of freezing during winter.

Replace Worn Components Early

Small ignition faults can often be repaired before they develop into larger problems.

Don't Ignore Fault Codes

Recurring error codes are often an early warning that your boiler needs attention.

Related Heating Guides

Boiler Losing Pressure

No Heating

No Hot Water

Frequently asked questions

If you can't find the answer to your question here, please don't hesitate to contact us for further assistance.

A boiler may fail to ignite because of low boiler pressure, a frozen condensate pipe, thermostat problems, ignition component failure, electrical issues or an interrupted gas supply. Identifying the underlying cause is the first step towards restoring your heating.

Clicking usually indicates that the ignition system is attempting to light the burner. If the boiler repeatedly clicks without igniting, the ignition electrode, flame sensor or gas supply may require professional inspection.

Yes. Many boilers will not ignite if the pressure falls below the recommended operating range. Check your pressure gauge and, if necessary, read our Boiler Losing Pressure guide to understand why the pressure may have dropped.

Yes, but only once. Most manufacturers recommend performing a single reset after checking the pressure and thermostat. If the boiler still won't ignite, repeated resets may make diagnosis more difficult and won't resolve the underlying fault.

Not always, but ignition faults should never be ignored. If you notice the smell of gas, burning odours or repeated lockouts, switch the boiler off and contact a Gas Safe engineer immediately.

A power interruption may reset your boiler or affect its controls. Check the electrical supply, reset the boiler once if recommended by the manufacturer and confirm that your thermostat is functioning correctly.

Yes. Keystone provides boiler ignition diagnostics and repairs throughout London. Our Gas Safe engineers work on all major boiler brands and can quickly identify faults affecting your heating or hot water.

The cost depends on the cause of the problem and whether replacement parts are required. Keystone provides transparent quotations after diagnosing the fault, so you'll know exactly what repair is needed before any work begins.

Yes. Our engineers repair and service leading manufacturers including Worcester Bosch, Vaillant, Ideal, Baxi, Glow-worm, Viessmann, Alpha, Potterton, Main and Vokera. Whether your boiler won't ignite, keeps locking out or displays fault codes, we can help restore your heating safely.

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