Overview
The C7 217 fault on a Worcester Bosch Greenstar I (System/Combi) means the boiler has detected that the combustion fan stopped while the appliance was running. The fan is critical for drawing combustion air and expelling flue gases; if it stops or runs at the wrong speed the boiler will shut down as a safety precaution. This code specifically indicates an airflow/fan interruption during operation rather than a simple start-up failure. Common causes are a seized or failed fan motor, debris or obstruction in the flue or fan housing, a loose or damaged wiring connector between the fan and the control PCB, or a fault on the control board itself. Severity is moderate to high: the boiler will typically lock out and must not be used until the fault is diagnosed because failed ventilation can allow dangerous flue gases to accumulate. Some basic checks and a reset can be done by a homeowner, but anything involving internal access, electrical testing, fan removal, or gas work should be left to a Gas Safe qualified engineer. Troubleshooting and diagnosis beyond simple external checks and rebooting should be performed by a competent, qualified engineer. Repeatedly forcing the boiler to run with a fan fault is unsafe and can cause further damage to the appliance.
Possible Cause: Fan has stopped during appliance operation.
Troubleshooting Steps
Safety precautions:
- If you smell gas or a carbon monoxide alarm is sounding, immediately turn off the gas supply if safe to do so, evacuate the property, ventilate by opening doors/windows, and call the gas emergency number (in the UK: 0800 111 999) or your local emergency services. Do not use the boiler.
- Do not open sealed compartments or attempt electrical tests or repairs unless you are a qualified Gas Safe engineer. Working on gas appliances or live electrical parts is dangerous.
- Make sure a working carbon monoxide detector is fitted nearby and operational before using the boiler again.
Initial homeowner checks (safe to do without opening the boiler):
1. Note the exact code shown (C7 217) and when it happened (during DHW, heating, or after running for a while).
2. Power-cycle the boiler: switch off at the isolator or fuse spur, wait 30–60 seconds, then switch back on. Attempt a reset using the boiler reset button if your model has one and follow the on-screen prompts. If the fault clears and does not return, monitor closely.
3. Listen at start-up: when you call for heating or hot water, stand near the boiler and listen for the fan. If you hear no fan noise during ignition or a weak/struggling sound, that points to a fan fault.
4. Check the flue terminal outside for obvious blockages (bird nest, leaves, debris) or signs of damage. Do this visually only — do not insert objects into the flue. Remove obvious external obstructions safely if possible.
5. Check mains power to the boiler and any external isolation switches. Ensure the boiler has a stable supply and no recent power interruptions occurred.
6. Check boiler pressure is in the normal range (around 1.0–1.5 bar when cold). Low pressure is not a primary cause of C7 but it's good to confirm the boiler is otherwise normal.
Further diagnostic information to collect for the engineer:
- Exact error code and any secondary numbers shown (C7 217), how often it occurs, and whether it happens on start-up or after running.
- Whether the boiler attempts to ignite, any noises (clicks, attempted fan spin), and whether the fault is intermittent or permanent.
- Take photos of the display and external flue terminal if safe.
What a qualified engineer will check/perform (do not attempt these yourself):
- Verify the fault code and use the boiler’s diagnostic mode/quick-info to read stored fault history.
- Test for fan operation: check fan wiring, connector, and supply voltage while operating. Measure fan motor electrical continuity and RPM/airflow as needed.
- Inspect fan assembly and flue path internally for seized bearings, debris, insect ingress, or mechanical obstruction. Clean or replace fan if necessary.
- Inspect and test the control PCB and connectors for faults or corrosion; replace PCB if confirmed faulty.
- Check any related safety sensors (flue thermostat, flow/return sensors) and bus communications that might falsely indicate a fan fault.
- After repairs, run the boiler and test for correct ignition, stable operation, and absence of flue gas leaks; confirm no further C7 codes are logged.
When to call a professional and final notes:
- If the C7 217 returns after a reset, the fan does not make any noise on start-up, or you are unsure about any step, turn the boiler off and call a Gas Safe registered engineer. Do not attempt internal electrical or gas repairs yourself.
- Provide the engineer with the fault code, a description of what you observed, and any photos. This speeds diagnosis and repair.
- Do not repeatedly reset and force the boiler to run if the fault persists — this risks unsafe operation and further damage.
If in doubt, contact a qualified Worcester-accredited or Gas Safe engineer to diagnose and repair the fan, wiring, or control board issue. The C7 217 is usually repairable but requires professional inspection to restore safe operation.
Helpful Resources
Boiler Manual
Download the official PDF manual for the Worcester Bosch Greenstar I System / Combi Boiler.