High
25 on Chaffoteaux Calydra 23 Green

Your boiler has lost communication with the sensor that monitors the hot water temperature in your storage cylinder, meaning it cannot safely heat your water.

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.

Technical description

Thermistor cylinder open

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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