Common problems guide

The most common Worcester Bosch 24i Junior problems

The faults most likely to send a Worcester Bosch 24i Junior into lockout — with plain-English causes, what to check first, estimated repair costs and whether you need a Gas Safe engineer.

This model is discontinued. Parts can be harder to source and expensive. If repair costs are mounting, a new A-rated boiler may be the smarter choice.

The 3 most common faults

01

Flash once per second High Engineer

Your boiler has stopped working because it has detected a safety issue and locked itself to prevent damage.

Est. cost: £120-250
Parts: Ignition lead, Electrodes, Printed Circuit Board

Full guide for Flash once per second

02

F1 High Engineer

Your boiler has stopped working because an internal safety fuse has failed, cutting off the electrical power to the system's control board.

Est. cost: £120-200
Parts: Internal fuse, Printed Circuit Board (PCB)

Full guide for F1

03

F2 High Engineer

Your boiler has stopped working because an internal electrical fuse has blown, cutting off the power needed for it to operate.

Est. cost: £120-200
Parts: Control PCB, Internal glass fuse, Wiring harness

Full guide for F2

Parts most often replaced

on the Worcester Bosch 24i Junior

Ignition leadElectrodesPrinted Circuit BoardHeat exchangerInternal fusePrinted Circuit Board (PCB)

Based on parts cited in our fault code database. Your engineer will confirm what's actually needed after diagnosis.

Call a Gas Safe engineer if…

You can smell gas or see signs of a leak
The Worcester Bosch shows an Emergency or High severity code
The boiler keeps locking out after repeated resets
You've tried the DIY checks and the fault hasn't cleared
There's visible water leaking from the boiler
The flame is yellow or orange instead of blue

See the full 3-code list for the Worcester Bosch 24i Junior