Common problems guide

The most common Worcester Bosch Worcester 25/30 HE problems

The faults most likely to send a Worcester Bosch Worcester 25/30 HE 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.
20 documented codes
6 most common
2 DIY-safe checks
4 engineer needed

The 6 most common faults

01
EA High DIY-safe

Your boiler has tried to light several times but has failed to detect a flame, causing the system to shut down for safety.

What to try first

Check if other gas appliances in your home, like a cooker, are working to ensure gas supply is active.If it is freezing outside, check that your white plastic condensate pipe is not frozen or blocked.Ensure your gas meter has credit and the emergency control valve is in the 'on' position.

Est. cost
£120-£350
Parts
Ignition Electrode, Flame Sensing Probe, Gas Valve
Full guide for EA
02
F0 High DIY-safe

Your boiler’s internal computer has encountered a software or communication glitch that is preventing it from running properly.

What to try first

Locate the reset button or dial on the boiler control panel.Press and hold the reset button for five seconds, then release.Wait up to 10 minutes for the boiler to restart and attempt to fire up.

Est. cost
£250-450
Parts
Printed Circuit Board (PCB), Wiring Loom
Full guide for F0
03
C1 High Engineer

Your boiler has stopped working because the fan that removes waste gases is not spinning fast enough to operate safely.

Est. cost
£220-£450
Parts
Fan assembly, Printed Circuit Board (PCB), Venturi tube
Full guide for C1
04
C4 High Engineer

Your boiler's internal fan is running constantly and won't shut down, preventing the system from starting its normal ignition sequence.

Est. cost
£180-450
Parts
Fan Assembly, Printed Circuit Board (PCB), Air Pressure Switch
Full guide for C4
05
C6 High Engineer

Your boiler's internal fan is spinning faster than it should, which has caused the system to shut down for safety.

Est. cost
£180-£450
Parts
Fan assembly, Printed Circuit Board (PCB), Harness wiring
Full guide for C6
06
d1 High Engineer

Your boiler has detected a problem with the sensor that monitors the temperature of the water returning to the unit, causing it to stop working for safety.

Est. cost
£100-£180
Parts
Return temperature sensor (NTC thermistor), Wiring harness, Control board (LSM module)
Full guide for d1
Parts most often replaced

on the Worcester Bosch Worcester 25/30 HE

Ignition ElectrodeFlame Sensing ProbeGas ValvePCBPrinted Circuit Board (PCB)Wiring Loom

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 20-code list for the Worcester Bosch Worcester 25/30 HE

Related guides

Boiler losing pressure → No hot water → When to replace → Symptom checker →