Medium Lockout
E04 on Ravenheat CSI 120

Your boiler has detected a problem with the sensor that monitors hot water temperature, meaning you will likely have no hot water or inconsistent temperatures.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Book a service

This fault should be looked at by a Gas Safe engineer within the next week or two. It may get worse if left.

Technical description

Domestic hot water (DHW) sensor damaged

What causes this fault?

This fault occurs when the internal sensor responsible for measuring the temperature of your hot water fails or sends an incorrect signal to the boiler’s control board. The most common reason is that the sensor has either burnt out over time or developed a lime-scale build-up that prevents it from reading the water temperature accurately.

Engineer required

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

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Related fault codes

E03View →E05View →E06View →

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