Ferroli Sigma Fault codes & diagnostics

6 fault codes with plain-English explanations, severity ratings, DIY guidance, and repair cost estimates.

Combi Natural Gas Discontinued

The fault code is already on your display

Note it down before pressing reset — resetting clears the code immediately. How to read fault codes →

Severity at a glance

Each cell = one fault code. Hover to identify.
1 Emergency 5 High
Just want the most common Ferroli Sigma faults?
The top 6 problems in plain English — with causes, DIY checks and repair costs.
Fault codes

All 6 documented codes

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Boiler lockout

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

High DIY-safe £120-280

What to check first

  1. Check that your gas supply is active and other gas appliances are working
  2. Press the 'Reset' button on the boiler control panel
  3. Check for any obvious obstructions in the external flue pipe outside your home

Parts commonly replaced

  • Ignition electrode
  • Gas valve
  • Printed Circuit Board (PCB)
Full explanation for Boiler lockout
Boiler sooting

Your boiler is not burning gas properly, which is causing a dangerous buildup of black soot and potentially harmful fumes.

Emergency Engineer only £120-300

Parts commonly replaced

  • Burner
  • Gas Valve
  • Air Intake Pipework
Full explanation for Boiler sooting
Burner fails to ignite

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

High Engineer only £120-350

Parts commonly replaced

  • Gas valve
  • Ignition electrode
  • Fan
  • Air pressure switch
Full explanation for Burner fails to ignite
Burner goes out

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

High Engineer only £100-280

Parts commonly replaced

  • Flow temperature sensor
  • Gas valve
  • Burner injectors
Full explanation for Burner goes out
Condensate in boiler

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

High Engineer only £120-280

Parts commonly replaced

  • Gas valve
  • Main burner
  • Condensate trap
Full explanation for Condensate in boiler
Radiators cold in winter

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.

High DIY-safe £120-350

What to check first

  1. Check that your room thermostat is turned up high enough to call for heat
  2. Ensure your programmer or timer is set to the 'On' position for heating
  3. Replace the batteries in your wireless room thermostat if the screen is blank

Parts commonly replaced

  • Circulation Pump
  • Flow Temperature Sensor (NTC)
  • Room Thermostat
Full explanation for Radiators cold in winter