Overview
The F7 228 on Worcester Bosch CDi Compact / Greenstar Si/i boilers means the flame detection system has seen a flame signal when the burner has not yet started (ionisation before ignition) or it is detecting a false flame. In plain terms the boiler thinks there is a flame at the wrong time. That can be caused by a faulty or dirty ignition electrode (the spark/ion probe), moisture or contamination on the electrode, damaged or loose wiring between the electrode and the control board, flue or earthing/grounding issues that allow a stray signal, or a control board (PCB) fault. In rare cases it can also follow brief power interruptions or component failures that confuse the flame sensing circuit. Severity: this is a safety-related fault and the boiler will usually lock out to prevent unsafe operation. It is not an immediate household emergency like a strong smell of gas, but it should not be ignored. Some simple checks and a single reset can clear a transient false alarm, but if the code persists you need a Gas Safe registered engineer to investigate and repair. Internal ignition parts, gas valves, wiring and PCB diagnosis and replacement must only be done by a qualified professional. DIY or professional: safe initial checks and a reset are reasonable for a homeowner. Do not attempt to dismantle the burner, replace ignition electrodes, test gas valves, or work on the PCB unless you are a trained Gas Safe engineer. If the fault returns after simple checks, switch the boiler off and call a qualified engineer.
Possible Cause: False flame or flame detected before burner started.
Troubleshooting Steps
Safety first
- If you smell gas: evacuate the property immediately, do not operate electrical switches, and call the gas emergency number and a Gas Safe engineer.
- If the boiler is showing F7 228 repeatedly, do not repeatedly try long sequences of resets; perform the simple checks below and contact a Gas Safe engineer if it persists.
- Unless you are qualified, do not remove the burner cover, attempt gas-valve testing, or replace ignition hardware. Isolate mains power at the fused spur before opening the case for visual checks, but non-technical users should avoid opening the boiler at all.
Initial homeowner checks (simple, safe):
1) Record the exact code and any other messages or behaviour (does it happen on both CH and HW demand, after cold start, after a power cut?). Take a photo of the display.
2) Try one controlled reset: follow the boiler manual or press the reset button once, wait for the boiler to attempt a normal start cycle. If the boiler restarts and runs normally for a period, monitor for recurrence.
3) Power-cycle: switch the boiler off at the front panel, isolate mains from the fused spur for about 60 seconds, then restore power and try again. Some transient electronic faults clear after a full power cycle.
4) Check for obvious water leaks or condensation ingress around the ignition area and electrode wiring (visible from front panel only). Moisture on the electrode or corroded connectors can cause false signals. If you see wetness, switch the boiler off and call an engineer.
5) Inspect the flue terminal externally for obvious blockages (nests, leaves, debris) that might affect sensor behaviour. Do not attempt to remove internal flue parts yourself.
6) Look for signs of rodent damage or chewed wiring near accessible external parts. Report any suspect wiring to the engineer.
If the fault continues or any of the following conditions are present, stop and phone an engineer:
- F7 returns after reset/power-cycle
- You find wet or corroded ignition electrode or wiring
- You see damaged or loose connectors on accessible plug-in leads
- The fault followed a power surge or lightning strike
What a Gas Safe engineer will check and do (for your information):
- Verify the fault memory and run diagnostic tests to reproduce the issue and timestamp behaviour.
- Inspect and if required clean or replace the ignition electrode/ionisation probe and its high-quality connector. The electrode gap and condition are critical for correct flame sensing.
- Check electrode wiring and earth/ground connections for continuity, short circuits, or insulation breakdown.
- Check the flue sensor and flue installation for any issues that could create spurious signals.
- Test the PCB inputs/outputs for correct voltages and behaviour; where the PCB is faulty it may need replacement.
- If applicable, perform gas valve leak/closure tests if the control system indicates an abnormal sequence (this must only be done by a qualified engineer).
- Run the boiler through several start/stop cycles and confirm safe operation before leaving.
Practical homeowner notes and final advice:
- Limit DIY to the basic checks above (reset, power-cycle, visual external/flue inspection). Do not attempt to clean or replace ignition components unless you are Gas Safe registered.
- If the error persists, switch the boiler off and contact a Gas Safe registered engineer. When you call, give them the boiler model, the exact fault code (F7 228), whether it cleared on reset, any visible moisture/damage, and when it started.
- Keep a record of fault occurrences and any actions taken—this helps the engineer diagnose intermittent issues quickly.
- Do not request or accept work from anyone not Gas Safe registered for gas appliance repairs or ignition/gas valve work.
Helpful Resources
No specific resources found.
Boiler Manual
Download the official PDF manual for the Worcester Bosch CDi Compact / Greenstar 25/30 Si Combi / Greenstar 27/30 I system Boiler.