Overview
E09 on a Potterton Assure combi or system boiler means the boiler has detected a fault in the gas valve connection cable or its electrical connection. In practice this code appears when the boiler’s control electronics cannot correctly communicate with or sense the gas valve: the cable, plug, connector pins, or associated wiring may be loose, broken, shorted to earth, corroded or otherwise faulty. Less commonly the fault can be caused by a failure on the PCB (control board) or an internal gas valve electronics failure that mimics a wiring fault. Severity is moderate to high because the boiler will typically lock out and refuse to light until the problem is resolved — this prevents unsafe gas delivery. While some non-invasive checks and a simple reset are safe for a homeowner to try, any work inside the appliance that involves exposing the gas valve, gas piping, or internal electrical terminals must be handled by a Gas Safe registered engineer. Replacing the gas valve or doing live electrical/gas repairs is not a DIY task.
Possible Cause: Gas valve connection cable fault
Troubleshooting Steps
Safety precautions:
1) If you are not confident working near gas or electrical equipment, stop and call a Gas Safe engineer. Do not attempt internal repairs on the boiler.
2) Before opening any cover, isolate the boiler from mains electrical supply. If you plan to access internal components, also isolate the gas supply and only proceed if qualified — otherwise leave internal checks to a Gas Safe engineer.
3) Ensure good ventilation and keep a clear escape route from the boiler area. Do not attempt to light or force the boiler to run while it reports E09.
Initial checks a homeowner can do (no internal opening required):
1) Note the exact error code and any other codes shown. Take photos of the fault display and note when it started and any recent events (power cut, work done, rodents, damp).
2) Try a basic reset: use the boiler reset button (hold 3–5 seconds) or switch the boiler off at the mains for 30 seconds then back on. If the code clears and does not return, monitor the boiler — intermittent faults often show up again.
3) Check household gas supply: confirm other gas appliances (cooker, gas fire) work. If there is no gas supply to the house, contact the gas supplier.
4) Check mains power to the boiler and fuses. Low voltage or power interruptions can cause communication faults.
5) Check for obvious external damage to wiring or controllers (room thermostat, programmer). If a wireless room controller has connection issues, try re-pairing or checking batteries.
Specific diagnostic and safe inspection steps (if you are competent and willing to proceed; always isolate mains before opening):
1) Isolate mains power to the boiler. If you have the skills to do so, isolate gas before removing the casing; otherwise don’t attempt internal work.
2) Remove the boiler front panel following manufacturer guidance. Visually inspect the cable and connector linking the PCB to the gas valve: look for loose plugs, bent/broken pins, corroded contacts, burn marks, melted insulation, or rodent chew damage.
3) Re-seat the connector: with power still isolated, carefully unplug the gas valve connector and plug it back in to ensure a secure contact. Do not force connectors or use excessive heat.
4) Inspect wiring continuity: if you have a multimeter and know how to use it safely, check continuity of the gas valve cable between the valve connector and the PCB connector. Also check for shorts to earth. If you find an open circuit, intermittent contact, or a short, the cable should be replaced.
5) Inspect the PCB connector: check for cracked solder joints, loose terminal screws or damaged traces. If the PCB looks burnt or damaged, note the board serial and error history and stop — PCB replacement or repair should be done by a qualified engineer.
6) After any re-seating or visible repairs, replace the cover, restore power and retry the boiler. Observe whether the E09 returns and note any other codes.
When to call a professional:
1) If E09 persists after a reset and simple visual checks, call a Gas Safe registered engineer. Any repair that requires replacing the gas valve, altering internal wiring, working on the PCB, or doing live gas/electrical work must be done by a Gas Safe engineer.
2) If you found damaged wiring, corrosion, a short, or a suspected PCB fault during inspection, stop and contact a Gas Safe engineer — provide them with the photos, error code history and any continuity readings you made.
3) If the boiler locks out repeatedly or other safety-related codes appear alongside E09 (flame faults, PCB errors, overheat), do not attempt further DIY.
Other practical notes:
1) Record the boiler model, serial number and exact fault code sequence to give to the engineer. Take clear photos of the connectors and wiring before calling for help.
2) Repeated transient E09 faults may be caused by vibration, damp, or intermittent connections; these are often fixed by replacing the cable or repairing the connector, but that work must be completed by a qualified engineer.
3) Never attempt to replace or adjust the gas valve or any gas-carrying component yourself. For safety and legal reasons, a Gas Safe registered engineer must carry out gas valve replacement and any commissioning or leak testing afterwards.
Helpful Resources
Boiler Manual
Download the official PDF manual for the Potterton Assure Combi and system.