Common problems guide

The most common Main Combi 24 problems

The faults most likely to send a Main Combi 24 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.
5 documented codes
5 most common
0 DIY-safe checks
5 engineer needed

The 5 most common faults

01
A Engineer

The flue or flue terminal is blocked or obstructed in some way, or there is an internal fault.

Full guide for A
02
B Engineer

The circulating pump is faulty or the system pressure has dropped. Check the system pressure.

Full guide for B
05
E Engineer

The burner has failed to light, or incomplete lighting of the burner has occurred.

Full guide for E

Call a Gas Safe engineer if…

  • You can smell gas or see signs of a leak
  • The Main 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 5-code list for the Main Combi 24

Related guides

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