Common problems guide

The most common Ferroli Optimax HE 31 C problems

The faults most likely to send a Ferroli Optimax HE 31 C 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.
32 documented codes
6 most common
3 DIY-safe checks
3 engineer needed

The 6 most common faults

01
Low system pressure High DIY-safe

Your boiler has stopped working because the water pressure inside your heating system has dropped too low to operate safely.

What to try first

Locate the external filling loop, usually a small braided metal hose connecting two pipes under the boilerOpen the valves at both ends of the hose to allow mains water to enter the system while watching the pressure gaugeClose both valves firmly once the needle sits between 1 and 1.5 barReset the boiler using the reset button on the control panel

Parts
Filling loop, Pressure relief valve, Expansion vessel
Full guide for Low system pressure
02
F37 High DIY-safe

Your boiler has stopped working because the water pressure inside the heating system has dropped too low to operate safely.

What to try first

Locate the external filling loop, which is a silver braided flexible hose connected to two valves under the boiler.Gradually open the valves to allow water into the system until the pressure gauge on the front of the boiler reads between 1.0 and 1.5 bar.Close both valves tightly and ensure the boiler resets itself.

Est. cost
£80-150
Parts
Filling loop, Pressure relief valve, Pressure sensor
Full guide for F37
03
F40 High DIY-safe

Your boiler has stopped working because the water pressure inside the heating system has dropped too low.

What to try first

Locate the filling loop, which is usually a silver braided hose under the boiler.Open the valves on both ends of the hose to let mains water into the system.Watch the pressure gauge on the front of the boiler and close the valves once the needle reaches 1.5 bar.

Est. cost
£80-120
Parts
Filling loop, Pressure relief valve, Pressure sensor
Full guide for F40
04
No burner ignition High Engineer

Your boiler is failing to light the flame needed to heat your water and home.

Est. cost
£120-250
Parts
Ignition electrode, Gas valve, PCB
Full guide for No burner ignition
05
A01 High Engineer

Your boiler is failing to light the fuel inside, meaning it cannot produce any heat or hot water for your home.

Est. cost
£120-250
Parts
Ignition electrode, Gas valve, Condensate siphon
Full guide for A01
06
A03 High Engineer

Your boiler has detected that it is overheating and has automatically switched itself off to prevent damage.

Est. cost
£120-250
Parts
Safety thermostat, Pump, Heat exchanger
Full guide for A03
Parts most often replaced

on the Ferroli Optimax HE 31 C

Filling loopPressure relief valveExpansion vesselPressure sensorIgnition electrodeGas valve

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 Ferroli 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 32-code list for the Ferroli Optimax HE 31 C

Related guides

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