Low
t4 on Worcester Bosch Greenstar CDi Compact

Your boiler is currently running a background self-test to ensure the internal component that switches between heating your radiators and heating your hot water is working correctly.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Monitor it

This is a minor fault. Keep an eye on it and mention it at your next annual boiler service. Reset the boiler and see if it clears.

What the manual says

Manufacturer manual

Three way valve test. Test the operation of the diverter valve. When 1 is selected via the test menu the diverter valve will move to the DHW position. When 0 is selected the valve will move to CH position.

From this model's manual
Verified against the Worcester Bosch Greenstar Cdi Compact 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 fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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