How to Fix Worcester Bosch F7 Fault Code (False Flame Signal) UK
Worcester Bosch F7 means false flame signal. UK diagnosis, parts to order, reset sequence.
What F7 means
Worcester Bosch F7 indicates false flame signal. The boiler will lock out and refuse to fire until the fault is cleared.
Do not simply reset — F7 is stored in the Worcester Bosch error log and will re-trigger within minutes if the underlying part has failed.
Diagnostic sequence
Enter service mode on the Worcester Bosch boiler and read the flow/return/DHW temperatures, fan PWM, ionisation current and pump speed.
Cross-reference against the Worcester Bosch technical manual — F7 typically points to two or three candidate parts.
- Check wiring harness continuity to the suspect sensor before condemning it.
- Isolate at the fused spur, discharge and re-inspect connectors.
- Measure resistance / voltage at the PCB plug per Worcester Bosch test procedure.
Parts to have on the van
Carry a set of NTC sensors, an ignition electrode kit and a fan for Worcester Bosch — these three parts clear >70% of F7 call-outs.
Recommission
After the fix, run the Worcester Bosch boiler through a full flow test, gas rate, and combustion analysis. Log to the Benchmark book to preserve manufacturer warranty.
Frequently asked questions
- Can I reset F7 without changing parts?
- Only if the fault has cleared (e.g. low pressure repressurised). Persistent F7 means a hardware failure.
- Which is the most common cause of Worcester Bosch F7?
- On Worcester Bosch boilers, F7 most often points to the sensor or actuator matching its meaning (false flame signal); check wiring and connector integrity first.
- Is a Gas Safe engineer required?
- Yes — any works past the boiler case seal require a Gas Safe registered engineer under UK law.
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