Error F.4

Safety precautions:

1) If you smell gas: do not operate electrical switches, do not use phones inside the property, open doors and windows, turn off the gas at the meter (if it is safe to do so), leave the building and call the gas emergency number and a Gas Safe engineer. Do not attempt internal repairs.

2) If there is no gas smell, always switch the boiler off at the programmer and the isolator before touching external pipes or visible components. Do not remove panels or internal covers unless you are a qualified engineer.

3) Never attempt to repair or replace gas valves, ignition electrodes, wiring, the PCB or other internal gas or electrical components yourself.

Initial homeowner checks (safe, non-invasive):

1) Check the display and note the exact code and any additional codes shown. Record when it happened and any recent events (power cut, meter work, freezing weather).

2) Try a boiler reset following the instructions in the boiler manual (usually a RESET button or switching off for 60 seconds and turning back on). If the boiler re-lights and runs normally, monitor for reoccurrence.

3) Confirm other gas appliances in the house work (hob, gas fire) to help determine if supply to the property is present. If none work, contact your gas supplier.

4) Check the boiler’s gas isolator tap (usually a small lever or valve on the gas pipe to the boiler) is open. If you are unsure how to identify it, leave it and call a pro.

5) Inspect the external flue terminal and air intake for obvious blockages (e.g., bird nest, debris, snow/ice). Clear any external debris if it is safe to do so.

6) In freezing weather check the condensate discharge pipe (often a plastic pipe terminating outside). If frozen, thaw it using warm (not boiling) water or a warm cloth. A blocked/iced condensate can cause ignition problems.

Specific diagnostic steps and non-invasive fixes:

1) After performing the initial checks, attempt another controlled reset. Note whether the boiler attempts to ignite and if the fault returns immediately or after a short period.

2) If ignition still fails and gas supply to the property is confirmed, visually inspect the visible electrode/ignition lead area only if you can do so without removing panels: look for heavy carbon buildup, loose connectors or obvious damage. Do not probe or touch live parts. If you see corrosion or broken parts, do not try to replace them—call an engineer.

3) Check for signs of water ingress or moisture around the boiler controls/PCB area (damp, corrosion). Moisture can cause misreading of flame detection and other faults—this will need a professional to diagnose and repair.

4) If the boiler reports related codes (F.28, F.29, F.54 etc.) or multiple faults persist, note them and provide this information to the engineer; it helps narrow diagnosis (for example F.28 often points to flame detection/ignition transformer/electrodes or gas pressure issues).

When to call a professional and what to tell them:

1) Call a Gas Safe registered engineer if the F.4 code remains after basic checks, if you find damaged ignition components, if there is any sign of gas supply problems, or if you detect moisture/damage on the PCB or wiring.

2) Do not attempt component replacement yourself. Repairs that commonly require a qualified engineer include replacing the ignition electrode or lead, testing/replacing the spark generator or ignition transformer, checking and adjusting gas inlet pressure or gas valve, testing the PCB and wiring, or clearing internal condensate/drain blockages.

3) When you contact the engineer, give them: boiler model (Vaillant EcoMax Pro 18/28E), serial number if available, exact fault code(s), what checks you have already carried out, whether other gas appliances work, and whether the condensate pipe was frozen/blocked.

Final note: F.4 is a clear ignition failure. It can sometimes be cured by simple actions (reset, clearing a frozen condensate, removing external blockage) but frequently requires a Gas Safe engineer to test gas pressure and safely inspect and replace ignition components or electronic controls. Prioritise safety and call a qualified engineer if in doubt.