Medium
D4 on Worcester Bosch Greenstar 25 Si Compact

Your boiler has detected that your radiators are not transferring heat properly, causing the water returning to the unit to be much cooler than the water leaving it.

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.

What the manual says

Manufacturer manual

Temperature difference between supply and return exceeding limit

From this model's manual
Verified against the Worcester Bosch/Worcester Bosch Greenstar Si Compact 6720807277 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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Related fault codes

EAView →

All 40 fault codes on the Greenstar 25 Si Compact

Seeing a different code? Every code this model can display, in one place.

8C9A9U376380800808810828A1A3A8b7C1C4C6C7CCCECFD1D3E2E3E4E5E9EAECEDEEEFF0F7FAFbFDH5TTB

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