Common problems guide

The most common Potterton Heatmax Combi problems

The faults most likely to send a Potterton Heatmax Combi 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.
14 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 correctly.

What to try first

Locate the filling loop (a flexible silver hose) underneath the boiler.Open the valves on the filling loop to allow cold mains water into the system.Watch the pressure gauge on the front of the boiler until the needle reaches the green zone (usually 1.0 to 1.5 bar).Close both valves tightly and remove the filling loop if it is a detachable type.

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

Your boiler is currently unable to read the temperature of the water being sent to your radiators, so it has turned off the heating to prevent any potential overheating.

Est. cost
£120-220
Parts
Central Heating NTC Sensor, Wiring harness
Full guide for E20
03
E28 High Engineer

Your boiler has detected an issue with the sensor that monitors the temperature of the gases leaving your flue, causing it to shut down for your safety.

Est. cost
£150-250
Parts
Flue NTC Sensor, Wiring harness
Full guide for E28
04
E50 High Engineer

Your boiler has lost the ability to accurately measure the temperature of the hot water it produces, so it has stopped heating water to prevent overheating.

Est. cost
£120-200
Parts
Domestic Hot Water (DHW) NTC Thermistor, Wiring Harness
Full guide for E50
05
E110 High Engineer

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

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

Your boiler has detected that hot water isn't moving around your radiators and pipes as it should, so it has shut down to prevent overheating.

Est. cost
£180-350
Parts
Circulation pump, Diverter valve, System filter
Full guide for E125
Parts most often replaced

on the Potterton Heatmax Combi

Pressure Relief ValveExpansion VesselPressure SensorCentral Heating NTC SensorWiring harnessFlue 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 Potterton 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 14-code list for the Potterton Heatmax Combi

Related guides

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