High
FU on Keston System S30

Your boiler is overheating because water is not flowing through your heating system properly to carry the heat away.

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.

What the manual says

Manufacturer manual

DIFF GREATER THAN 50ºC. CHECK ISOLATION VALVES ARE OPEN, CHECK PUMP, CHECK RAD VALVES OPEN, CHECK SYSTEM BLOCKAGES

From this model's manual
Verified against the Keston System S30 installation & service manual.
Plain-English guidance below. Severity, DIY steps, costs and parts are our interpretation to help you act, not text from the manual.

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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