Boiler Not Firing Up: Lockouts and Ignition Faults

Is it being asked to fire?

Turn the thermostat up well above the room temperature, set the timer to constant or boost, and run a hot tap if you have a combi. If nothing happens at all and the display is blank, check the fused spur switch near the boiler and the consumer unit.

If the display is on but there is no sound of the fan or ignition, the boiler may not be receiving a call for heat. A wireless thermostat with flat batteries is a common reason.

Is it getting gas and enough pressure?

A boiler will not light without gas and will refuse to run if the pressure is too low:

• Try your gas hob, if you have one, to confirm gas is reaching the house
• On a prepayment meter, check there is credit and the supply has not cut off
• Make sure the gas valve under the boiler is open (handle in line with the pipe)
• Check the pressure gauge; most boilers need around 1 bar or more when cold

What a lockout means

A lockout is a safety shutdown. The boiler has tried to light, failed, or sensed something wrong, and stops until someone resets it. The display normally shows a code or a flashing light. Write it down before you do anything; it tells an engineer a lot.

Pressing reset once is fine. If the boiler locks out again, do not keep resetting it. Repeated attempts will not fix the cause and can make it harder to diagnose.

Frozen condensate pipe

In cold weather, the plastic condensate pipe that runs outside can freeze, the water backs up and the boiler locks out, sometimes with a gurgling sound. Pour warm water, not boiling, slowly along the outside section of the pipe, then reset the boiler. This is the most common cause of a boiler not firing up in a cold snap.

Not firing up with no error code

If there is no code and the boiler simply does nothing, look at the controls first: the timer, thermostat and any smart controls. A faulty wiring centre or thermostat can stop the call for heat ever reaching the boiler.

If you hear clicking or the fan running but no ignition, the fault is more likely inside, such as the ignition electrode, the flame sensor, the gas valve or the fan. Those parts are for a Gas Safe registered engineer only.

Older boilers, including back boilers behind a fire, may have a pilot light that has gone out. Relighting should only be attempted following the instructions on the boiler itself. If the pilot will not stay lit, stop and get it checked.

Need it sorted? Book a boiler repair

Have the boiler make, model and fault code ready, then call or WhatsApp 07429 632804. See our boiler repairs page, or emergency boiler repair if you have no heating or hot water. Non-urgent? Use the quote form.