High
F5 on Ideal Logic Combi ESP1

Your boiler's internal sensor that monitors the temperature of the water coming back into the unit has developed a fault, preventing the system from operating correctly.

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

Return Thermistor Fault

From this model's manual
Verified against the Ideal Logic Combi Esp1 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.

What causes this fault?

This fault occurs when the boiler's internal computer stops receiving a reliable signal from the sensor that monitors the temperature of the water returning from your radiators. The most common reason is that the sensor itself has worn out or suffered an electrical failure, meaning it can no longer tell the boiler if it is safe to continue heating.

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

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