High
H4 on Ideal Icos

Your boiler has detected that it is not sensing the correct temperature in the main heat exchanger, likely due to a faulty sensor or a internal electrical connection issue.

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

ALTERNATING 'H' '4' (REFER TO FRAME 71)

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

H1View →

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