Error F.00

Safety precautions:

1) If the boiler is displaying F.00, turn off the boiler normal way first, then switch off the electrical isolator to the boiler. Do not attempt internal electrical or gas work unless you are a Gas Safe registered engineer. 2) Avoid touching internal components while the boiler has power. 3) If you smell gas or suspect a gas leak, leave the property immediately and call the gas emergency number. 4) If you are unsure about any step, stop and call a Gas Safe engineer.

Initial homeowner checks you can do (no internal or electrical work):

1) Try a boiler reset using the manufacturer’s reset procedure shown in the user manual or on the boiler controls. Note whether the fault returns immediately or after a short run. 2) Check the system pressure on the boiler display; if pressure is very low (below about 1 bar) top up following the user manual instructions, then try reset again. 3) Check for obvious signs of damage or loose wiring on the outside of the boiler such as crushed cables or a visibly disconnected terminal outside the sealed casing. 4) Confirm the heating demand: ensure room thermostat/timers or hot water demand are set to call for heat so the boiler will try to run and reproduce the fault. 5) Note any recent work, knocks, burst pipes or power surges—these can cause wiring or PCB faults.

Diagnostic steps a qualified engineer will perform (for information only):

1) Verify fault history on the boiler controller and reproduce the fault if possible. 2) Isolate electrical supply and remove the boiler service cover following safe working practices. 3) Visually inspect the flow NTC connector and the wiring harness for corrosion, damaged insulation, chafing, or a pulled connector; reseat the plug to the PCB and check that all nearby plugs are correctly seated (some F.00/F.01 faults are caused by loose plugs). 4) With the wiring accessible, an engineer will measure continuity of the harness and the resistance of the NTC thermistor at ambient temperature with a multimeter. A healthy NTC should show a resistance that changes with temperature; an open circuit or short indicates a faulty cable or thermistor. 5) If wiring and sensor check out, the engineer will check that the PCB is reading the sensor input correctly; occasional PCB faults can cause false sensor error codes. 6) If a defective component is confirmed, the engineer will replace the failed part (NTC, cable/harness or PCB) and re-test the system under run conditions. 7) After repair, the engineer will check for proper operation, correct temperature rise, and clear the fault code and monitor for reoccurrence.

When to call a professional and final notes:

1) If a simple reset does not clear F.00, or the fault returns, call a Gas Safe registered heating engineer. 2) Do not attempt to replace the NTC, wiring or PCB yourself if you are not qualified; work inside the boiler exposes you to live electrical parts, gas, and sealed components. 3) Explain to the engineer that the F.00 code indicates a flow NTC interruption so they can bring appropriate diagnostic tools and parts. 4) The likely fixes are reconnecting a loose plug, replacing a damaged wiring harness, replacing the flow NTC thermistor, or in rarer cases replacing the PCB. 5) If the boiler has other concurrent fault codes (e.g., F.91, F.23), mention those as they help the engineer diagnose related sensor or circulation issues.