How much does it cost to fix Baxi error code H.01 – .18?

Typical repair cost for the Baxi H.01 – .18 fault is £120-£350 including labour.

H.01 – .18 High

Baxi H.01 – .18 Fault Code

Q: What does the Baxi H.01 – .18 fault code mean?

Your boiler has stopped working because water is not moving through the system properly or a temperature sensor has detected an overheating issue.

Also written as H0118 — same fault.

The Baxi H.01 – .18 fault code means: your boiler has stopped working because water is not moving through the system properly or a temperature sensor has detected an overheating issue.. It appears on 24 Baxi models in our database.

Technical description: No water circulation, insufficient circulation or sensor error.

What causes the Baxi H.01 – .18 fault?

This fault occurs when the boiler's internal sensors detect that heat is not being carried away from the burner quickly enough, leading to an overheat risk. The most common reasons are a failed pump that isn't pushing water around, or a blockage caused by sludge and debris inside the pipework or heat exchanger. In some cases, it may simply be caused by a faulty sensor sending an incorrect temperature reading to the main control board.

This issue often surfaces during the first cold snap of autumn when a pump that has been idle all summer fails to restart or struggles to move thickened sludge through the radiators.

Typical repair cost £120-£350 (including labour)

DIY fix possible

Check that your boiler pressure is between 1.0 and 1.5 bar on the internal gauge.Ensure all radiator valves and any isolation valves under the boiler are fully open.Attempt to reset the boiler by turning the selector switch to the reset position for five seconds.Bleed your radiators to remove any trapped air that may be blocking circulation.

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Baxi models that show the H.01 – .18 fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Baxi H.01 – .18 fault code information on this page is sourced and cross-checked against the official Baxi service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026