Common problems guide

The most common Main System 24 Eco problems

The faults most likely to send a Main System 24 Eco 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.
9 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 has dropped too low to operate safely.

What to try first

Locate the external filling loop, which is a flexible braided hose usually found underneath the boiler.Open the small valve or tap attached to the hose slowly until you hear water entering the system.Watch the pressure gauge on the front of the boiler until the needle reaches the green zone, typically between 1.0 and 1.5 bar.Close the valve or tap tightly and ensure no water is dripping from the hose.

Est. cost
£80-150
Parts
Pressure Relief Valve, Pressure Sensor/Switch, Expansion Vessel
Full guide for E119
02
E20 High Engineer

Your boiler has stopped heating because it is unable to accurately measure the temperature of the water circulating through your radiators.

Est. cost
£120-180
Parts
Central Heating NTC Sensor, Wiring harness
Full guide for E20
03
E28 High Engineer

Your boiler's computer module does not match the specific settings or version required for your model, meaning the system cannot communicate correctly to heat your home.

Est. cost
£250-450
Parts
Printed Circuit Board (PCB)
Full guide for E28
04
E50 High Engineer

Your boiler has lost the ability to accurately measure the temperature of the water, so it has turned itself off as a precaution to prevent overheating.

Est. cost
£120-200
Parts
Hot Water NTC Sensor, Wiring Harness
Full guide for E50
05
E110 High Engineer

Your boiler has switched itself off because it has detected an overheating issue, which prevents it from running until it cools down and the fault is cleared.

Est. cost
£120-250
Parts
Safety limit thermostat, Pump, Diverter valve
Full guide for E110
06
E125 High Engineer

Your boiler is struggling to pump water around your heating system, likely because the water isn't flowing freely or the pump is stuck.

Est. cost
£150-300
Parts
Central heating pump, Flow sensor, System diverter valve
Full guide for E125
Parts most often replaced

on the Main System 24 Eco

Pressure Relief ValvePressure Sensor/SwitchExpansion VesselCentral Heating NTC SensorWiring harnessPrinted Circuit Board (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 9-code list for the Main System 24 Eco

Related guides

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