Low
4-b5 on Worcester Bosch Greenstar 2000

Your boiler is notifying you that its internal protection against freezing has been activated or deactivated, which is a normal safety monitoring function.

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

Device frost protection: OFF: switched off, ON: switched on.

From this model's manual
Verified against the Worcester Bosch Greenstar 27cdi 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.

DIY fix possible

Check your home temperature is above 5°CEnsure the boiler power supply remains switched onMonitor the display to see if the code clears once the unit reaches a safe temperature

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