Common problems guide

The most common Ariston Genus 24 MFFI problems

The faults most likely to send a Ariston Genus 24 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.
73 documented codes
6 most common
2 DIY-safe checks
4 engineer needed

The 6 most common faults

01
2 - CIRCULATION FAILURE High DIY-safe

Your boiler has detected that water is not circulating properly around the system, so it has safely shut itself down to prevent damage.

What to try first

Check your boiler pressure gauge and ensure it is between 1 and 1.5 barIf the pressure is low, locate the filling loop and add water until it reaches the correct levelBleed your radiators to remove any trapped air that may be blocking the flow

Est. cost
£120-250
Parts
Circulation pump, Pressure switch, Diverter valve
Full guide for 2 - CIRCULATION FAILURE
02
NO WATER L.E.D. High DIY-safe

Your boiler has detected that the water pressure inside your heating system is too low to operate safely.

What to try first

Locate the external filling loop, which is usually a silver braided hose under the boiler.Open the valves on the filling loop to allow water into the system until the pressure gauge reads 1.5 bar.Close the valves firmly and check for any leaks around the filling loop connections.

Est. cost
£80-150
Parts
Pressure relief valve, Pressure sensor, Expansion vessel
Full guide for NO WATER L.E.D.
03
A01 High Engineer

Your boiler has failed to light because it cannot detect a steady gas supply, so it has safely shut down to prevent gas from leaking into your home.

Est. cost
£120-250
Parts
Ignition electrode, Gas valve, PCB
Full guide for A01
04
UU/FF High Engineer

Your boiler is failing to detect a flame, which means it cannot safely light or stay running to provide you with heat and hot water.

Est. cost
£120-250
Parts
Ionisation electrode, Ignition lead, PCB
Full guide for UU/FF
05
UU/tt High Engineer

Your boiler is struggling to detect the flow of water circulating through the system, which prevents it from igniting to provide you with heat or hot water.

Est. cost
£150-250
Parts
Flow switch, Diverter valve diaphragm, Microswitch
Full guide for UU/tt
06
AA0011 High Engineer

Your boiler has failed to start up because it could not light the internal flame after several attempts.

Est. cost
£120-250
Parts
Ignition electrode, Gas valve, PCB
Full guide for AA0011
Parts most often replaced

on the Ariston Genus 24 MFFI

Circulation pumpPressure switchDiverter valvePressure relief valvePressure sensorExpansion vessel

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 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 73-code list for the Ariston Genus 24 MFFI

Related guides

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