BoilerFaultCodesThe 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 filling loop (usually a silver braided hose with one or two valves) underneath your boiler.Gradually open the valve(s) to allow mains water into the system while watching the pressure gauge on the front of the boiler.Stop the flow once the needle reaches the green zone (typically between 1.0 and 1.5 bar) and ensure the valve is firmly closed.
02
E20 High Engineer
Your boiler has stopped heating your home or water because it is failing to read the internal temperature correctly.
Full guide for E2003
E28 High Engineer
Your boiler has detected that the internal control board is not the correct version required for your specific model, preventing it from functioning safely.
Full guide for E2804
E50 High Engineer
Your boiler has lost the ability to accurately measure the temperature of the hot water inside it, so it has shut down to prevent overheating.
Full guide for E5005
E110 High Engineer
Your boiler has detected that it is overheating and has shut itself down to prevent internal damage.
Full guide for E11006
E125 High Engineer
Your boiler has detected that water is not flowing around your heating system correctly, which prevents it from safely producing heat.
Full guide for E125on the Potterton Apollo
Pressure relief valvePressure sensorExpansion vesselNTC Temperature 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 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