Error F0

Safety precautions:

1) If you smell gas, stop using any naked flames, do not switch electrical items on or off, ventilate by opening doors and windows, evacuate the property and call the gas emergency number immediately. Do not try to investigate internal gas components yourself.

2) Always isolate the boiler from the mains supply before attempting any inspection that involves removing covers or touching internal components. If you are not competent or not Gas Safe registered, do not remove the boiler casing or touch gas/electrical parts.

3) Do not repeatedly reset the boiler if faults reoccur; excessive resetting can be unsafe and may mask a developing hazard. If a locking fault persists, call a professional.

Initial checks a homeowner can safely do:

1) Check the boiler’s electrical supply: ensure the mains isolator and any fused spur to the boiler are switched on and the household fuseboard hasn’t tripped. Check other appliances on the same circuit to confirm power is present.

2) Check the programmer/room thermostat: make sure the heating/cylinder settings are calling for heat and batteries (where applicable) in thermostats are good. A lack of demand can sometimes be misinterpreted as a fault when the boiler is fine.

3) Perform a controlled reset: press and hold the boiler reset button for about 3 seconds and release to attempt a restart. If that does not clear it, some manuals advise holding reset for 10 seconds, waiting 30 seconds, and trying again. After reset, observe if the F0 returns immediately or after a specific action (e.g., when calling for heat or hot water).

4) Look and smell for obvious signs of trouble without opening the casing: any visible water leak under/around the boiler, scorch marks, burn smells or loose external wiring route are reason to stop and call an engineer.

5) Simple power-cycle: switch the boiler off at the mains isolator, leave off for about 30 seconds and then switch back on, then try the reset procedure again.

Specific diagnostic steps and what they mean (professional actions flagged):

1) If the F0 persists after safe resets and power-cycling, note down the exact fault code (F0) and any additional cause/three-digit codes shown in the information menu (press the spanner/return or information button if your model provides this). Take a clear photo of the display and any flashing LEDs—this helps the engineer.

2) Check ignition leads visually only: some F0 reports reference ignition/ionisation leads. From the outside you can look for obvious disconnected or damaged external wiring where the boiler wiring enters, but do not remove panels or probe internal leads. If you see loose external connectors on terminal blocks that are accessible without removing covers, you may gently tighten them only if you are competent and the boiler is isolated from mains.

3) Check external controls and wiring: confirm the room thermostat, programmer and any external switching circuits are plugged in and operating. Loss of a programming interface or wrong wiring can cause internal communication faults.

4) Professional-only diagnostics and fixes (call a Gas Safe registered engineer): the engineer will open the boiler safely and check connector contacts, plug-in modules (HCM/KIM), the PCB, ignition and ionisation circuits, and the gas valve coils. They will reseat/connect or replace the faulty control module, repair damaged wiring or replace defective PCBs or burner control units where necessary. They will also test for gas valve integrity and leaks and conduct safe operational checks after repair.

When to call a professional and what to tell them:

1) Call a Gas Safe registered heating engineer if the F0 does not clear after the basic safe checks and resets, if you find visual signs of damage or water ingress, or if you detect any gas smell. Do not attempt internal repairs yourself.

2) When you call, provide boiler make, model and serial number, the exact fault code (F0) and any secondary cause codes from the info menu, a description of when the fault appears (on demand, intermittently, after power cycle), and any observations (leaks, burn smell, visible damage). Send the photos you took of the display and the boiler exterior if possible.

Summary: You can safely try power and reset checks and basic external visual inspections, but an F0 points to an internal electrical/control issue and usually requires a Gas Safe registered engineer to properly diagnose and repair the control module, PCB, connectors or ignition circuits. If you smell gas or find signs of a leak or fire damage, evacuate immediately and call the emergency gas service.