The control board has detected an internal fault or a communication problem.
Most common on: Greenstar i, CDi Classic
D5 indicates an internal control-board fault — the PCB has detected a problem with itself or with communication between components.
It is not a homeowner fix. After a reset to rule out a glitch, it needs an engineer to test and usually replace the PCB.
Hold reset to rule out a one-off glitch.
A recurring D5 needs board-level diagnosis by a Gas Safe engineer.
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.
TradePlanr turns the callout into paid work — log the job, quote the parts and labour, raise the gas safety record and send the invoice from your phone, even with no signal. Free to start, works in your browser, no download needed.
The control board has detected an internal fault or a communication problem. D5 indicates an internal control-board fault — the PCB has detected a problem with itself or with communication between components.
You can try a single reset and the safe checks below, but Worcester Bosch D5 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 D5 means the underlying cause has not been fixed — most often faulty pcb. Resetting repeatedly will not solve it; get the boiler diagnosed properly.
See all Worcester Bosch fault codes.