High
FAIL POINT E on Worcester Bosch Greenstar 25Si

Your boiler has lost the ability to detect when you turn on a hot water tap, meaning it cannot start the heating process correctly.

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.

Technical description

Flowswitch assembly fault, multiway connector ST16 contacts 19 and 20 (pink wires) continuity issue, or damaged Red diode on control board.

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.

Find a Gas Safe engineer
Search the official register →

Related fault codes

Related guides you might find useful