How much does it cost to fix boiler error code L4?

Typical repair cost for the boiler L4 fault is £90-160 including labour.

L4 High

Boiler Fault Code L4

Reviewed by the BoilerFaultCodes Editorial Team Last reviewed 31 August 2026

Fault code L4 appears across 4 boiler brands and 20 models. The exact meaning varies by manufacturer — pick your boiler brand below to see the model-specific fix.

Most common meaning Your boiler has detected a problem with the internal sensor that monitors the temperature of the water as it leaves the unit, causing the system to shut down as a safety precaution. (As reported on Ideal Logic Combi ESP1)

Pick your boiler brand for the L4 fix

Baxi L4 1 model Ideal L4 17 models Keston L4 1 model Zanussi L4 1 model

Source

Information for the L4 fault code is sourced from the official service / installation manual for each model that displays it. Read more about how we source fault codes →

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 31 August 2026