Common problems guide

The most common Ferroli Sigma 40 FF problems

The faults most likely to send a Ferroli Sigma 40 FF 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.

The 6 most common faults

01

Boiler lockout High Engineer

Your boiler has stopped working because it cannot light the flame after several attempts, meaning you currently have no heating or hot water.

Est. cost: £120-250
Parts: Ignition electrode, Ignition lead, Printed Circuit Board (PCB)

Full guide for Boiler lockout

02

Burner fails to ignite High Engineer

Your boiler is trying to start but the flame is not catching, meaning it cannot produce any heat or hot water.

Est. cost: £150-350
Parts: Flow temperature sensor, Gas valve, Air pressure switch

Full guide for Burner fails to ignite

03

Burner goes out High Engineer

Your boiler is struggling to keep its flame lit, which means it cannot heat your water or home reliably.

Est. cost: £120-250
Parts: Flow temperature sensor, Gas valve, Burner assembly

Full guide for Burner goes out

04

Condensate in boiler High Engineer

Your boiler is struggling because your water temperature is set too low, which is causing damaging moisture to build up inside the unit.

Est. cost: £120-250
Parts: Condensate trap, Gas valve

Full guide for Condensate in boiler

05

Radiators cold in winter High Engineer

Your boiler is struggling to push warmth around your home because the internal parts responsible for moving or measuring hot water are not working as they should.

Est. cost: £150-300
Parts: Central heating pump, NTC thermistor sensor

Full guide for Radiators cold in winter

06

Fan runs boiler does not work High Engineer

Your boiler is attempting to start its fan but cannot complete the ignition process, meaning it cannot provide you with heating or hot water at this moment.

Est. cost: £120-250
Parts: Air pressure switch, Fan assembly, PCB

Full guide for Fan runs boiler does not work

Parts most often replaced

on the Ferroli Sigma 40 FF

Ignition electrodeIgnition leadPrinted Circuit Board (PCB)Gas valveFlow temperature sensorAir pressure switch

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 12-code list for the Ferroli Sigma 40 FF