Error FB 365

Safety first

1) If you smell gas or suspect a strong gas leak: do not operate electrical switches, do not use phones or open flames in the property. Open doors and windows, evacuate everyone from the building and call your local gas emergency service immediately (in the UK call 0800 111 999). Call a Gas Safe registered engineer to attend.

2) If there is no smell of gas but the boiler shows FB 365, treat it as a potential gas safety issue and do not attempt internal repairs. Keep the boiler turned off until an engineer can inspect it. Ensure any occupants have working CO alarms and evacuate if a CO alarm sounds.

Initial homeowner checks you can safely do

1) Make a note or photograph of the exact error code (FB 365), any other codes, and the boiler model/serial number and location. This speeds up the engineer’s diagnosis.

2) Check for obvious external signs: check that the flue terminal outside is unobstructed and that there are no visible signs of damage to external pipework or fittings. Do not remove covers from the boiler.

3) If your boiler has been reset automatically or you have recently experienced power interruptions, you may try a single manual reset following the manufacturer’s guidance (consult the boiler manual). Do not repeatedly press reset. If the code returns immediately or after a short time, stop resetting.

4) If you smell gas at any time, follow the emergency steps above and do not delay calling the gas emergency service.

What a professional engineer will do (diagnostic and fix steps they follow)

1) Confirm the fault using diagnostic menus and any logged cause codes. They will repeat the manufacturer leak test procedure in a controlled way.

2) Check the gas supply and inlet pressure, and verify there is no external gas leak at fittings and pipework feeding the boiler.

3) Electrically test the gas valve EV1: measure coil resistance, check wiring and connector integrity, and verify correct operation from the PCB during the test sequence.

4) Perform a controlled leak test across EV1 (as per Worcester procedure) and check for physical leaks or seating problems. They will use calibrated instrumentation and safe procedures only trained engineers should perform.

5) If EV1 is confirmed leaking or mechanically faulty, the gas valve assembly will normally be replaced with a correct OEM part and the replacement assembled/commissioned by the engineer. After replacement they will test operation, run safety checks and confirm correct ignition and flame sensing.

6) If the valve electrical control is correct but the PCB is suspect, the engineer will investigate control board faults and replace or repair components as required.

7) After repair the engineer will perform full safety checks: gas tightness testing, burner/combustion checks, flue checks, return to service and record the work performed.

Important homeowner guidance and final notes

1) Do not attempt to open the boiler casing, remove or dismantle the gas valve, or make internal electrical repairs. These are gas work and require a Gas Safe registered engineer.

2) A single reset attempt is acceptable if you are following the manual, but repeated resets are unsafe and will not fix a true gas valve leak. If FB 365 persists, turn the boiler off and call a Gas Safe engineer.

3) If you smell gas at any time, evacuate and call the gas emergency service immediately. If a CO alarm activates, evacuate and call the emergency services and a Gas Safe engineer.

4) Prepare information for the engineer: model and serial number, time/date the fault started, any other error codes, and whether you smelled gas. This helps the engineer diagnose faster.

5) This fault is treated as a serious safety issue. A qualified Gas Safe (or local equivalent) registered heating engineer must be called to diagnose and repair the underlying problem.