Common problems guide

The most common Ferroli Sigma problems

The faults most likely to send a Ferroli Sigma 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.
8 documented codes
6 most common
3 DIY-safe checks
3 engineer needed

The 6 most common faults

01
Boiler lockout High DIY-safe

Your boiler has failed to light several times and has locked itself out for safety.

What to try first

Check that your gas supply is active and other gas appliances are workingPress the 'Reset' button on the boiler control panelCheck for any obvious obstructions in the external flue pipe outside your home

Est. cost
£120-280
Parts
Ignition electrode, Gas valve, Printed Circuit Board (PCB)
Full guide for Boiler lockout
02
Radiators cold in winter High DIY-safe

Your central heating system is failing to warm up your radiators because water isn't being circulated correctly or the system isn't being told to turn on.

What to try first

Check that your room thermostat is turned up high enough to call for heatEnsure your programmer or timer is set to the 'On' position for heatingReplace the batteries in your wireless room thermostat if the screen is blank

Est. cost
£120-350
Parts
Circulation Pump, Flow Temperature Sensor (NTC), Room Thermostat
Full guide for Radiators cold in winter
03
37 High DIY-safe

Your boiler has stopped working because the amount of water inside your heating system has dropped too low.

What to try first

Locate the filling loop, which is a silver braided hose usually found underneath the boiler.Open the valves at both ends of the hose to let mains water into the system.Watch the pressure gauge on the front of the boiler until the needle reaches the green zone (usually around 1.5 bar).Close both valves tightly and remove the filling loop if it is not a permanent fixture.

Est. cost
£80-150
Parts
Pressure relief valve, Pressure sensor, Expansion vessel
Full guide for 37
04
Burner fails to ignite High Engineer

Your boiler is unable to light the flame needed to heat your water and radiators.

Est. cost
£120-350
Parts
Gas valve, Ignition electrode, Fan
Full guide for Burner fails to ignite
05
Burner goes out High Engineer

Your boiler is struggling to stay lit because it is either dirty or isn't getting a steady flow of gas.

Est. cost
£100-280
Parts
Flow temperature sensor, Gas valve, Burner injectors
Full guide for Burner goes out
06
Condensate in boiler High Engineer

Your boiler is producing excess moisture internally because it is running too cool or burning gas at the wrong rate.

Est. cost
£120-280
Parts
Gas valve, Main burner, Condensate trap
Full guide for Condensate in boiler
Parts most often replaced

on the Ferroli Sigma

Ignition electrodeGas valvePrinted Circuit Board (PCB)Circulation PumpFlow Temperature Sensor (NTC)Room Thermostat

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 8-code list for the Ferroli Sigma

Related guides

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