Overview
The C1 264 fault on a Worcester Bosch Greenstar i (system/combi) indicates the boiler detected that airflow stopped while the fan was supposed to be running. The fan is essential for drawing air for combustion and forcing flue gases out of the appliance; if it stops or the air pressure switch does not see the expected pressure change, the boiler will shut down as a safety precaution. The code typically points to a failed fan motor, an electrical/wiring fault to the fan, a blocked or obstructed flue/airway, or a fault with the air pressure switch or PCB circuitry that monitors the fan. Severity is moderate to high because the boiler has intentionally shut down to prevent unsafe combustion or flue gas being forced back into the home. That shutdown protects you, but it also means no heating or hot water until the fault is resolved. Some simple checks and resets can be done by a homeowner, but any internal electrical, gas, or component work should only be carried out by a Gas Safe–registered engineer. If you suspect a gas smell or carbon monoxide, evacuate, ventilate, and contact the gas emergency number immediately rather than attempting troubleshooting.
Possible Cause: Fan stopped during operation.
Troubleshooting Steps
Safety precautions:
- If you smell gas or suspect carbon monoxide (soot, headache, dizziness), leave the property immediately, call the gas emergency line, and do not operate the boiler. Ensure you have a working CO alarm near the boiler and sleeping areas.
- Turn the boiler off at the programmer and the isolator switch before attempting any visual checks. Do not remove the boiler casing or touch internal components unless you are a qualified Gas Safe engineer.
Initial homeowner checks (safe to do):
1. Reset the boiler: try the boiler reset procedure per the user manual (usually press and hold the reset button or switch off at the isolator for 1–2 minutes, then turn back on). Note whether the C1 264 returns immediately or after a short run.
2. Check external flue terminal and air inlet: go outside and make sure the flue termination and any air inlet vents are clear of leaves, bird nests, rubbish, snow or ice. Remove light debris at the terminal if safe to do so.
3. Check surrounding area: ensure the boiler’s air vents (if fitted) and the area around the boiler are not blocked by stored items, dust or heavy dirt. Keep the area clean and ventilated.
4. Condensate/frost check (cold weather): if temperatures are below freezing, a frozen condensate pipe can sometimes affect operation—inspect visible condensate piping for ice. Thawing should be done by running warm water over the external length or calling an engineer.
5. Note behavior: record when the code appears (on start, during operation, intermittently), any unusual noises (fan trying to run but stalling), or recent events (service overdue, power interruption, building work nearby).
Specific diagnostic and likely fixes (for a qualified engineer):
- Visual and electrical checks: the engineer will isolate the boiler, remove the casing and inspect fan assembly, connectors and wiring for damage, loose plugs, corrosion or pinched cables. They will check the fan plug and connector at the PCB.
- Test fan operation: measure supply to the fan, test fan motor operation and RPM. If the fan is not receiving supply or is not running correctly it will be repaired or replaced.
- Air pressure switch and hose: inspect and test the air pressure switch and the associated hose/ducting between the fan and switch for blockages, splits, or disconnection. Replace or clean as required.
- Flue integrity and obstruction: check the flue path inside and outside for blockages or damage and verify the flue sensor readings if applicable.
- PCB diagnostics: if wiring and fan are good, the engineer will test the PCB signals to/from the fan and air pressure switch. A faulty PCB or intermittent contacts may require replacement.
- Reassembly and functional test: after repairs or part replacement the engineer will reassemble, run the boiler through several start/stop cycles, and verify safe operation. They may perform flue gas checks where required by regulation.
When to call a professional:
- If the reset does not clear the fault or the code returns repeatedly, call a Gas Safe–registered engineer. Any internal inspection, electrical tests, fan motor replacement, pressure switch work or PCB work must be done by a qualified professional.
- Call immediately if you smell gas, suspect carbon monoxide, or if there are signs of soot, unusual burning smells or symptoms affecting occupants.
Preventive advice:
- Arrange annual servicing by a Gas Safe engineer to keep the fan, airways, pressure switch and PCB in good order. Keep the flue terminal and air vents clear of obstruction and maintain a clean area around the boiler.
Note: the steps above are meant to help you understand likely causes and safe preliminary checks. Do not open the boiler or attempt internal repairs yourself—only a Gas Safe registered engineer should carry out live electrical, mechanical or gas work.
Helpful Resources
Boiler Manual
Download the official PDF manual for the Worcester Bosch Greenstar I System / Combi Boiler.