Error F0 278

Safety precautions:

1. If you smell gas, evacuate the property, call the gas emergency number and do not operate any electrical switches or the boiler.

2. Before doing any work on the boiler, switch it off at the programmer and isolate mains power at the fused spur or consumer unit. If you are not confident isolating electrical supply, do not proceed and call an engineer.

3. Do not attempt to access or repair gas valves, burners, or internal PCB components unless you are a Gas Safe registered engineer. Do not work on the boiler while it is live.

Initial homeowner checks you can safely do:

1. Record the exact error code and any cause code or triangle/lock symbol shown on the display.

2. Try a basic reset: with the boiler powered on, press the reset (spanner/return) button once. If the fault clears and the boiler runs, monitor for recurrence. If it returns, proceed to further checks.

3. Power-cycle the boiler: isolate mains power for at least 60 seconds, restore power and check if the error returns. This can clear transient electronic faults.

4. Visually inspect the outside of the boiler and area around it for signs of water leaks, corrosion, or damp that could have reached the electronics or wiring. Check that no wiring is visibly pinched or damaged where it exits the casing.

5. Check external controls: if you have a room thermostat, wireless receiver or control module, ensure batteries are good and any connectors between the thermostat and the boiler are secure. A missing or faulty code plug/KIM module or loose connector on an external control can cause sensor/communication errors.

Specific diagnostic and fix steps (what a technician will do and what you can report to them):

1. If initial checks did not clear the fault, do not attempt internal electrical tests yourself. Contact a Gas Safe engineer and provide them the fault code F0 278 and a description of any visual issues and the steps you have already tried (reset, power-cycle, signs of damp).

2. The engineer will isolate the boiler and remove the casing to visually inspect the burner control unit (KIM), sensor plugs and wiring looms for loose connectors, corrosion, water ingress or physical damage.

3. They will measure sensor resistances and continuity with a multimeter to identify open circuits, short circuits or out-of-spec thermistor values (flow sensor, return sensor, safety sensor etc.). Sensors commonly checked include the flow NTC, return NTC and safety/limit sensors.

4. If a faulty connector, pinching, or water in the control box is found, the engineer will clean/repair the connector and dry or replace damaged wiring as required. If a sensor is defective it will be replaced and retested.

5. If the control unit / KIM or PCB is suspected (F0 family codes can indicate A/D converter or control-board issues), the engineer will test the A/D inputs and, if necessary, replace the burner control unit or PCB and re-run the sensor test.

6. After repairs, the engineer will clear the fault code and run the boiler through ignition and temperature tests to confirm normal operation. They should leave you with details of the fault, what was replaced and any recommendations to prevent recurrence (e.g. address leaks or improve condensate run-off to avoid water ingress).

When to call a professional:

1. Call a Gas Safe registered engineer if the error does not clear after reset/power-cycle, if you see signs of water ingress, or if you are not fully confident performing the safe visual checks listed above.

2. Any internal electrical testing, sensor replacements, or PCB/KIM interventions must be done by a Gas Safe engineer.

Final note: F0 278 often points to wiring/connector or sensor problems that an engineer can diagnose and fix, but because the repair requires working inside the boiler with electrical and gas systems present, a qualified Gas Safe technician should complete the diagnosis and repair. Provide the engineer with the exact fault code and a brief summary of any checks you have already done to speed up the process.