Common problems guide

The most common Chaffoteaux Duo problems

The faults most likely to send a Chaffoteaux Duo 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 4 most common faults

01

Fig. 15 High Engineer

Your boiler is failing to detect when you turn on a hot tap, meaning it isn't firing up to heat the water.

Est. cost: £150-250
Parts: Flow switch, DHW sensor, Diverter valve

Full guide for Fig. 15

02

Fig. 16 Emergency Engineer

Your boiler is releasing excess water outside through a safety pipe because the pressure inside the system has become too high.

Est. cost: £150-300
Parts: Pressure relief valve, Expansion vessel

Full guide for Fig. 16

03

Fig. 17 Emergency Engineer

Your boiler is releasing excess water because the internal pressure is too high or the safety valve has been triggered to prevent damage from overheating.

Est. cost: £150-300
Parts: Pressure relief valve, Pressure relief discharge pipe, Expansion vessel

Full guide for Fig. 17

04

Fig. 14 Medium Engineer

Your boiler is struggling to provide a steady supply of hot water to your taps, usually due to a build-up of debris or internal blockage.

Est. cost: £150-300
Parts: DHW Heat Exchanger, Flow Turbine, DHW Sensor

Full guide for Fig. 14

Parts most often replaced

on the Chaffoteaux Duo

Flow switchDHW sensorDiverter valvePressure relief valveExpansion vesselPressure relief discharge pipe

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 Chaffoteaux 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 4-code list for the Chaffoteaux Duo