Common problems guide

The most common Worcester Bosch 28 i SI problems

The faults most likely to send a Worcester Bosch 28 i SI 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.
6 documented codes
6 most common
0 DIY-safe checks
6 engineer needed

The 6 most common faults

05
K Engineer

Light indication during fault not covered by other details; control board likely wet or damaged.

Full guide for K
06
L Engineer

Gas valve mode switch incorrect, hot water sensor faulty, or gas pressure incorrectly set.

Full guide for L

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 6-code list for the Worcester Bosch 28 i SI

Related guides

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