Common problems guide

The most common Baxi Combi Instant 80/105 HE problems

The faults most likely to send a Baxi Combi Instant 80/105 HE 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.
25 documented codes
6 most common
1 DIY-safe checks
5 engineer needed

The 6 most common faults

01
27 High DIY-safe

Your boiler has stopped working because it either doesn't have enough water inside the system to operate safely or the internal water pump is failing to move the water around.

What to try first

Check your boiler's pressure gauge on the front panel; if it is below 1.0 bar, use the filling loop to top the system up to between 1.0 and 1.5 barEnsure your central heating system does not have any obvious water leaks coming from radiators or the boiler itselfOnce pressure is restored, reset the boiler using the reset button on the control panel

Est. cost
£120-250
Parts
Central heating pump, Pressure gauge, Pressure sensor
Full guide for 27
02
24 High Engineer

Your boiler has stopped working because it cannot light the flame or clear away waste water properly.

Est. cost
£120-250
Parts
Condensate trap, Ignition electrode, Gas valve
Full guide for 24
03
26 High Engineer

Your boiler has detected an issue with the system that blows out waste gases, meaning it has safely shut down to prevent unsafe operation.

Est. cost
£150-350
Parts
Fan assembly, Air pressure switch, Venturi
Full guide for 26
04
29 High Engineer

Your boiler has stopped working because it is unable to accurately measure the temperature of the water used for your radiators.

Est. cost
£120-200
Parts
Central Heating NTC Sensor
Full guide for 29
05
布 neon flashing High Engineer

Your boiler has stopped working because it cannot detect the water circulating inside, meaning it is preventing itself from firing up to stay safe.

Est. cost
£150-300
Parts
Central heating pump, Flow switch microswitch, Diverter valve diaphragm
Full guide for 布 neon flashing
06
© neon flashing High Engineer

Your boiler's temperature sensor is providing incorrect readings, which prevents the unit from heating your water or home correctly.

Est. cost
£120-220
Parts
NTC Temperature Sensor
Full guide for © neon flashing
Parts most often replaced

on the Baxi Combi Instant 80/105 HE

Central heating pumpPressure gaugePressure sensorCondensate trapIgnition electrodeGas valve

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 Baxi 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 25-code list for the Baxi Combi Instant 80/105 HE

Related guides

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