High Lockout
25 on Potterton Performa 30 HE

Your boiler has switched itself off because it has detected that a part inside has become too hot to operate safely.

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

Safety Thermostat Activated (Boiler or Flue)

What causes this fault?

This fault occurs when the water inside the boiler reaches an unsafe temperature, triggering a safety switch to kill the power. The most common reasons are a failed pump that isn't moving water away fast enough, or a build-up of limescale and sludge that has blocked the heat exchanger.

This issue often surfaces during the first cold spell of winter when the boiler is suddenly pushed to work at its maximum capacity after sitting idle all summer.

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.

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