Error E86

Safety precautions:

1) If you smell gas, leave the property immediately and call the gas emergency number — do not investigate the boiler. 2) Isolate electrical power at the boiler isolator or fuse before touching wiring or opening any panels. 3) Do not attempt gas or PCB replacements yourself — leave those tasks to a Gas Safe engineer. 4) Take photos or note exact error codes and the sequence/timing of events to give to an engineer.

Initial checks a homeowner can do (no tools or minimal tools):

1) Note any other fault codes shown alongside E86 and the time the fault appeared. 2) Check mains electricity to the boiler — is the display lit? Check the house fuse box and any external isolator switch. 3) Check that any external controls (room thermostat, programmer, smart hub) are powered and calling for heat. For wireless thermostats, check/replace the batteries and ensure the thermostat is set to request heating. 4) Try a controlled reset: press and hold the boiler reset button (or follow your model’s reset procedure) for the recommended time (typically 3–10 seconds). Wait for the boiler to attempt restart and see if the E86 clears. 5) If the boiler has been recently worked on, check that any external controls or wiring were reconnected properly.

If the fault persists: diagnostic steps and possible fixes (only attempt the wiring checks if you are competent and comfortable with isolating the mains first):

1) Power-cycle the boiler: switch off at the isolator/fuse box, wait 30–60 seconds, then restore power. Sometimes communication faults clear after a full power-down. 2) Check the room thermostat and programmer: temporarily set the thermostat to a high temperature or set the programmer to call for CH/DHW to see if the boiler responds. If the thermostat is wireless, check the receiver at the boiler is powered and paired. 3) For wireless systems: re-pair the thermostat and receiver following the manufacturer’s instructions; replace batteries in the thermostat; move the thermostat closer to the boiler temporarily to rule out RF range issues. 4) Inspect visible wiring and connectors (only after isolating electrical supply): look for loose or corroded terminals at the thermostat, programmer, or boiler terminals. Tighten loose screw terminals and reseat plugs that may have come partly out. 5) If you can safely and confidently do so, test by making a direct call for heat at the boiler control terminals (some installers/testers briefly link the CH call terminal to the live or insert a known working thermostat) to confirm whether the boiler operates when it receives a direct demand. Do not perform this test if you are unsure — isolating and shorting live terminals is hazardous.

When to call a professional and what to tell them:

1) Call a Gas Safe-registered engineer if E86 returns after resets, if the fault is intermittent, if you find damaged wiring, if the boiler will not provide heating/hot water, or if you are not confident performing the safe checks above. 2) Provide the engineer with the exact fault code(s), when they appeared, what steps you tried (reset, power-cycle, battery replacement, pairing attempts), and any other symptoms (no display, other error codes, noises, water leaks). 3) The likely engineer actions will include checking the thermostat/programmer wiring and RF module, testing or replacing the receiver or room unit, and diagnosing the PCB and internal communications; a PCB or module swap may be required if the board or receiver has failed.

Additional notes:

1) Avoid repeatedly resetting the boiler more than a couple of times if the code keeps returning — persistent lockouts should be investigated by an engineer. 2) While E86 is primarily an electrical/communications fault rather than a direct gas safety fault, it can leave you without heating or hot water — arrange prompt professional attention if you cannot restore normal operation.