A general internal fault, usually a temperature sensor reading out of range or a wiring fault.
Most common on: Greenstar i, CDi Classic
F0 is a general internal fault code. Most often it points to a temperature sensor (flow or return NTC) giving a reading the board cannot make sense of, or a wiring/connection problem.
It can sometimes be cleared with a reset, but a recurring F0 needs an engineer to test the sensors and wiring.
Hold the reset button. If F0 clears and does not return, it may have been a transient glitch.
Sensor and PCB testing needs a heating engineer with a multimeter and the service manual — not a homeowner fix.
Work on the gas side of a boiler must be carried out by a Gas Safe registered engineer. The checks above are limited to safe, non-invasive things a homeowner can look at (pressure, resets, the gas supply) — if in doubt, stop and call an engineer.
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A general internal fault, usually a temperature sensor reading out of range or a wiring fault. F0 is a general internal fault code. Most often it points to a temperature sensor (flow or return NTC) giving a reading the board cannot make sense of, or a wiring/connection problem.
You can try a single reset and the safe checks below, but Worcester Bosch F0 usually needs a Gas Safe registered engineer. Never work on the gas side of a boiler yourself — it is illegal and dangerous unless you are Gas Safe registered.
A recurring F0 means the underlying cause has not been fixed — most often faulty flow or return temperature sensor (ntc). Resetting repeatedly will not solve it; get the boiler diagnosed properly.
Overheat — primary temperature too high
Pump / circulation fault (dry fire protection)
See all Worcester Bosch fault codes.