Common problems guide

The most common Ferroli Optima 201 problems

The faults most likely to send a Ferroli Optima 201 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.
10 documented codes
6 most common
1 DIY-safe checks
5 engineer needed

The 6 most common faults

01
LED 1 green (0) High DIY-safe

Your boiler is currently completely unresponsive because it is not receiving any electrical power.

What to try first

Check that the boiler isolator switch (usually a white switch near the boiler) is set to the ON position.Check your home's main fuse box (consumer unit) to see if any circuit breakers have tripped.Locate the fused spur next to the boiler and check if the replaceable fuse inside has blown.

Est. cost
£80-150
Parts
External fuse, Fused spur switch, Printed Circuit Board (PCB)
Full guide for LED 1 green (0)
02
LED 2 yellow (0) [DHW mode] High Engineer

Your boiler does not realise that you have turned on your hot water tap, so it is failing to heat the water for your shower or kitchen faucet.

Est. cost
£120-220
Parts
DHW Flow switch, Microswitch
Full guide for LED 2 yellow (0) [DHW mode]
03
LED 4 green (0) [DHW mode] High Engineer

Your boiler has stopped producing hot water because it believes the internal temperature sensor is either disconnected or reading an dangerously high temperature.

Est. cost
£120-200
Parts
DHW NTC Sensor, Wiring harness
Full guide for LED 4 green (0) [DHW mode]
04
LED 5 red (1) [DHW mode] High Engineer

Your boiler has detected an internal computer error and is currently unable to start, meaning you will likely have no hot water or heating.

Est. cost
£250-400
Parts
Printed Circuit Board (PCB)
Full guide for LED 5 red (1) [DHW mode]
05
LED 4 green (0) [CH mode] High Engineer

Your boiler has stopped producing heat because it is struggling to accurately read its own internal temperature or has overheated.

Est. cost
£120-220
Parts
Central heating NTC temperature sensor, Limit thermostat, Wiring harness
Full guide for LED 4 green (0) [CH mode]
06
LED 6 yellow (0) [CH mode] High Engineer

Your boiler has detected a faulty temperature reading caused by a sensor issue, which is preventing your central heating from turning on.

Est. cost
£120-200
Parts
Central heating NTC temperature sensor
Full guide for LED 6 yellow (0) [CH mode]
Parts most often replaced

on the Ferroli Optima 201

External fuseFused spur switchPrinted Circuit Board (PCB)DHW Flow switchMicroswitchDHW NTC Sensor

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 10-code list for the Ferroli Optima 201

Related guides

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