High
E12 on Potterton Promax 15/2 HE Plus

Your boiler has detected that the water leaving the unit is significantly hotter than the water returning to it, often indicating a blockage or a pump issue that prevents water from circulating correctly.

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

Differential temperature too high (flow/return)

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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Related fault codes

E13View →E14View →E16View →

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