Common problems guide

The most common Ariston ACO 27 MFFI problems

The faults most likely to send a Ariston ACO 27 MFFI 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.
30 documented codes
6 most common
0 DIY-safe checks
6 engineer needed

The 6 most common faults

01
E08 Engineer

boiler shutdown both in D.H.W.mode and C.H.mode due to under floor heating thermostat contact opening

Full guide for E08

Call a Gas Safe engineer if…

  • You can smell gas or see signs of a leak
  • The Ariston 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 30-code list for the Ariston ACO 27 MFFI

Related guides

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