High
Return Thmr Fault on Keston Heat 45

Your boiler's temperature sensor at the water return pipe is faulty or disconnected, causing the system to stop heating because it cannot accurately measure the water temperature.

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.

What the manual says

Manufacturer manual

Check Return Thermistor Wiring, Check Return Thmr

From this model's manual
Verified against the Keston Heat 45 installation & service manual.
Plain-English guidance below. Severity, DIY steps, costs and parts are our interpretation to help you act, not text from the manual.

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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