How much does it cost to fix Keston error code 4.9?

Typical repair cost for the Keston 4.9 fault is £120-200 including labour.

4.9 High

Keston 4.9 Fault Code

Q: What does the Keston 4.9 fault code mean?

Your boiler has lost the ability to accurately measure the temperature of the water returning to it from your radiators, so it has shut down to prevent potential overheating.

Also written as 49 — same fault.

The Keston 4.9 fault code means: your boiler has lost the ability to accurately measure the temperature of the water returning to it from your radiators, so it has shut down to prevent potential overheating.. It appears on 1 Keston model in our database.

Technical description: RETURN THERMISTOR FAULT

Typical repair cost £120-200 (including labour)

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Keston models that show the 4.9 fault code

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

C30 / C35 Repair: £120-200

Source

Keston 4.9 fault code information on this page is sourced and cross-checked against the official Keston service / installation manuals for each affected model.

Keston C30 / C35 manual (PDF)

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026