Error 4 red flashes

Safety precautions:

- If you smell gas or carbon monoxide, evacuate the property immediately, call the emergency gas number and emergency services if necessary. Do not stay in the house.

- Before doing any checks, switch the boiler off at the control panel and, if possible, isolate electrical supply at the fuse spur. Do not open the boiler casing or attempt internal repairs unless you are a Gas Safe registered engineer.

- Do not repeatedly reset the boiler. One or two resets to clear a temporary fault are acceptable; repeated resets are unsafe and can make diagnosis harder.

Initial homeowner checks you can safely do:

1. Check the boiler display and note the fault: 4 red flashes (fan fault). Write down any other codes or lights.

2. Check the flue terminal outside the building for obvious blockages: birds’ nests, leaves, snow or ice. If you can safely remove small debris from outside, do so. Do not insert objects into the flue.

3. In very cold weather check for a frozen condensate pipe (if visible externally). If frozen, thaw using warm (not boiling) water or a warm cloth. Do not use open flames or high heat.

4. Make sure external vents around the boiler and air supply to the boiler are clear.

5. Confirm the boiler has normal electrical supply: check the fuse spur, RCD, and that other electrics in the house work. If the boiler has tripped an RCD, reset that and then try the boiler reset.

6. Listen at the boiler during a restart attempt for any fan noise, whistling, or rattling which can indicate a mechanical failure.

7. Check system pressure (on the boiler gauge) and top up to the manufacturer’s recommended 1–1.5 bar if it is low — while low pressure is not a primary cause of a fan fault, low pressure and poor circulation can cause other faults and are worth correcting before calling an engineer.

Reset procedure (one attempt):

- Locate the boiler reset control (button or selector). Hold/reset as manufacturer instructs (typically 5–10 seconds) and allow the boiler to attempt a restart. If the boiler clears and runs normally, monitor for recurrence. If the 4-red-flash fault returns, do not keep resetting.

Further diagnostic notes and what a professional will likely check:

- If external checks and a single reset do not fix it, the likely causes are: failed fan motor, faulty fan speed sensor, wiring/connector fault between fan and PCB, or a PCB fault misreading fan signals. An engineer will test fan operation, measure fan speed/impedance, inspect connectors and harnesses, check the flue sensor (if fitted), and test the PCB inputs.

- If the flue was blocked and has now been cleared, the engineer will confirm fan operation and run combustion checks. If the condensate pipe was frozen and thawed, an engineer should confirm no other damage to components.

When to call a professional and what to tell them:

- Call a Gas Safe registered engineer if the fault persists after the checks and single reset, or if you are uncomfortable performing the safe external checks. Do not allow anyone uncertified to work on gas appliances.

- When you call, tell them: boiler make/model, serial number if available, exact fault (4 red flashes / fan fault), what checks you carried out (flue cleared, condensate thawed, pressure topped up, reset attempted), any noises heard, and when the fault started. Take photos of the fault lights and of the flue terminal if helpful.

Final reminder: because the fan is part of the combustion safety system, a persistent fan fault requires professional diagnosis and repair. Avoid opening the boiler or attempting electrical/mechanical repairs yourself. Ensure you have working carbon monoxide detectors near fuel-burning appliances and follow the engineer’s advice for repair and follow-up safety checks.