Common problems guide

The most common Main Combi 28 problems

The faults most likely to send a Main Combi 28 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.
13 documented codes
6 most common
1 DIY-safe checks
5 engineer needed

The 6 most common faults

01
E119 High DIY-safe

Your boiler has stopped working because the water pressure inside the system is too low to operate safely.

What to try first

Locate the filling loop (usually a silver braided hose under the boiler).Open the valves to allow mains water into the system until the pressure gauge reads between 1.0 and 1.5 bar.Close both valves tightly to stop the flow of water.

Est. cost
£80-120
Parts
Pressure Relief Valve, Pressure Transducer, Expansion Vessel
Full guide for E119
02
Flame Failure High Engineer

Your boiler has stopped working because it failed to light or lost its flame during operation, so it has turned itself off for safety.

Est. cost
£120-250
Parts
Ignition Electrode, Gas Valve, Control PCB
Full guide for Flame Failure
03
Overheat High Engineer

Your boiler has detected that it is getting too hot and has automatically shut itself down to prevent damage.

Est. cost
£120-250
Parts
Pump, NTC Thermistor, Diverter Valve
Full guide for Overheat
04
E20 High Engineer

Your boiler has lost the ability to accurately measure the temperature of the water circulating through your radiators, so it has shut down to protect the system.

Est. cost
£120-220
Parts
Central Heating NTC Sensor, Wiring Harness
Full guide for E20
05
E28 High Engineer

Your boiler has detected a communication issue with the sensor that monitors the temperature of the gases leaving your flue, causing it to stop working to ensure your safety.

Est. cost
£120-200
Parts
Flue NTC Sensor, Wiring Harness
Full guide for E28
06
E110 High Engineer

Your boiler has detected that it is getting too hot and has automatically switched itself off to prevent damage.

Est. cost
£120-250
Parts
Pump, Diverter Valve, Primary Heat Exchanger
Full guide for E110
Parts most often replaced

on the Main Combi 28

Pressure Relief ValvePressure TransducerExpansion VesselIgnition ElectrodeGas ValveControl PCB

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 Main 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 13-code list for the Main Combi 28

Related guides

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