Error 6 flashes green

Safety precautions:

1) If you smell gas or suspect a carbon monoxide issue, turn off the boiler and gas supply immediately, ventilate the property, leave the building and call the gas emergency number or emergency services. Do not attempt repairs. 2) Always isolate electrical power at the isolator or fuseboard before removing panels. 3) Only a Gas Safe registered engineer should work on gas components, the combustion unit, gas valve, or PCB. Do not attempt to replace the combustion control unit yourself unless you are qualified.

Initial homeowner checks (safe, non-invasive):

1) Note the exact behaviour and timing of the 6 green flashes and any other LEDs or display messages. Record model and serial number and take a photo of the error. 2) Try a basic reset: follow your boiler’s reset procedure (press dedicated reset button or set selector to R and hold for 5 seconds). Wait and observe if the fault clears and whether the boiler runs normally. 3) Check mains power and gas supply: confirm other gas appliances work and that the electrical supply and any external timers/thermostats are on. 4) Check for obvious external blockages to the flue, visible condensate pipe freezing, or obvious signs of water ingress, damage or scorch marks on the boiler casing. These are simple visual checks only.

Simple diagnostic steps a homeowner can safely perform:

1) After power-isolating, remove the outer case only if the manufacturer’s manual permits and you are comfortable doing so. Do not touch gas pipes or internal electrical connections. 2) Do a visual inspection for obvious signs of burnt components, melted wiring, loose connectors, or water damage around the PCB and combustion module. Take photos. 3) If you see a loose plug or connector you can safely reseat it (only if the boiler is isolated). Refit the case, restore power and attempt a reset. Note: do not bend or force connectors and do not probe boards with tools.

What to do if the fault persists:

1) If reset and visual checks do not clear the 6-green-flash fault, do not continue attempts to run the boiler. The likely remedy is replacement/repair of the combustion control unit or further diagnosis of the PCB and associated wiring. 2) Contact a Gas Safe registered engineer and provide them with: boiler model/serial, the exact error (6 green flashes), what you’ve tried, and any photos or notes. 3) If the boiler has an action log or display diagnostic codes in addition to the LED flashes, note those and pass them to the engineer — they speed diagnosis.

Why you need a professional and final notes:

1) The combustion control unit regulates ignition, gas valve timing and flame sensing; faults here affect safety and require specialist knowledge, calibrated test equipment and Gas Safe competence. 2) A qualified engineer will test gas pressures, flame signals, fan operation, wiring/connector integrity and will replace the combustion control unit or PCB if required. 3) While some internal connection reseating may be safe, replacement of the PU/CSU or PCB must be done by a professional. Keep the boiler off until an engineer confirms it is safe to run.

If at any point you detect a gas smell, symptoms of carbon monoxide (headaches, nausea, flu-like symptoms when at home), or any leak, turn off the boiler and gas, ventilate, leave the property and contact emergency services/gas emergency and get professional help immediately.