BoilerFaultCodesThe 6 most common faults
01
118 High DIY-safe
Your boiler has stopped working because the water pressure inside the heating system has dropped too low to operate safely.
What to try first
Locate the external filling loop (a flexible silver hose) beneath the boiler.Open the valves at both ends of the hose to allow water into the system.Watch the pressure gauge on the front of the boiler until the needle reaches the green zone (typically 1.0 to 1.5 bar).Close both valves tightly and ensure the pressure gauge stays stable.
02
20 High Engineer
Your boiler has detected an internal communication error between its main electrical parts and has shut down as a safety precaution.
Full guide for 2003
28 High Engineer
Your boiler has detected an internal communication error and has safely shut itself down to prevent further damage.
Full guide for 2804
40 High Engineer
Your boiler has detected an internal communication error between its main electrical parts and has shut down as a safety precaution.
Full guide for 4005
160 High Engineer
Your boiler has detected an internal communication error and has safely shut down to prevent further issues.
Full guide for 16006
321 High Engineer
Your boiler has detected a communication error between its internal parts and has stopped working to prevent further damage.
Full guide for 321on the Potterton Assure
Filling loopPressure relief valvePressure sensorPrinted Circuit Board (PCB)Wiring HarnessWiring harness
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
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