High
D4 341 on Worcester Bosch Greenstar Ri

Your boiler is shutting down because the water inside is heating up much faster than the system can move it around, which usually points to a blockage or a pump issue.

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

Primary flow temperatures rising too fast

From this model's manual
Verified against the Worcester Bosch Greenstar Ri installation & service manual, page 67.
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 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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