High Lockout
25E on Ravenheat HE 80/90 / 25-30s

Your boiler has detected that the water inside the main heating unit has frozen, which is preventing the system from operating to avoid damage.

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

Main heat exchanger frozen

What causes this fault?

This fault occurs when the temperature sensor inside the boiler detects that the water within the heat exchanger has reached freezing point. The most common cause is the boiler being located in an unheated area like a garage or loft during a cold snap without adequate frost protection. It can also be triggered if the external condensate drainage pipe reflects a blockage caused by ice, preventing the system from circulating safely.

This fault is almost exclusively seen during the winter months when external temperatures drop below freezing for extended periods.

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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