High Lockout
E125 on Potterton Gold Combi HE

Your boiler has shut down because it is getting too hot inside, usually because the water isn't moving around the system properly.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

Technical description

Boiler temperature exceeded (circulation pump or air locked)

What causes this fault?

This fault occurs when the water inside the boiler reaches an unsafe temperature because it isn't being moved away into your radiators or hot water tap quickly enough. The most common reason is that the internal pump has failed or is stuck, but it can also be caused by a large air bubble trapped in the pipework blocking the flow.

This fault often appears at the start of autumn when the heating is turned back on after being off all summer, which can cause the pump to seize.

Engineer required

This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

Find a Gas Safe engineer
Search the official register →

Related fault codes

E110View →E130View →

Related guides you might find useful

Banging / kettling / whistling noise

Each noise points to a different fault.

Read →

Boiler won't turn on — 9-step checklist

Work through these before the call-out.

Read →

Boiler keeps cutting out

Lockout fault with a reset-needed pattern.

Read →