High
A LED 4 on Ferroli Optima 201

Your boiler has stopped providing hot water because it is having trouble reading the water temperature 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

- D.H.W. sensor (42) not connected or D.H.W. temperature too high

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

A01View →

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