Common problems guide

The most common Worcester Bosch 28 RSF problems

The faults most likely to send a Worcester Bosch 28 RSF 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 6 most common faults

01

Lock-out High Engineer

Your boiler is failing to light the flame properly, so it has purposefully shut down to prevent gas from building up inside.

Est. cost: £150-300
Parts: Ignition electrode, Gas valve, Ignition lead

Full guide for Lock-out

02

CH light On High Engineer

Your boiler has automatically turned itself off because the water inside it is getting too hot, likely due to a circulation problem.

Est. cost: £120-250
Parts: Pump, Heat exchanger, NTC sensor

Full guide for CH light On

03

DHW light High Engineer

Your boiler has automatically turned off because the hot water inside it has become dangerously hot.

Est. cost: £150-300
Parts: NTC Temperature Sensor, DHW Heat Exchanger, Diverter Valve

Full guide for DHW light

04

FAIL POINT A High Engineer

Your boiler is not receiving any power, meaning it cannot start up to provide your home with heating or hot water.

Est. cost: £120-250
Parts: Control PCB, Main Fuse

Full guide for FAIL POINT A

05

FAIL POINT B High Engineer

Your boiler has stopped working because a critical internal electrical component has failed, cutting power to the system's main brain.

Est. cost: £200-350
Parts: Control board, Transformer, Fuse F2

Full guide for FAIL POINT B

06

FAIL POINT C High Engineer

Your boiler is currently waiting for a signal from your heating controls, but it isn't receiving the instruction to turn on.

Est. cost: £120-250
Parts: Programmer, Room thermostat, Control board

Full guide for FAIL POINT C

Parts most often replaced

on the Worcester Bosch 28 RSF

Ignition electrodeGas valveIgnition leadPumpHeat exchangerNTC sensor

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 23-code list for the Worcester Bosch 28 RSF