D4286 High

Worcester Bosch D4286 Fault Code

The Worcester Bosch D4286 fault code means: your boiler has shut down because it thinks the water returning to the unit is dangerously hot, which usually means water isn't circulating through your radiators properly.. It appears on 1 Worcester Bosch model in our database.

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

Technical description: The boiler return temperature sensor has detected a return temperature higher than 105°c

What causes the Worcester Bosch D4286 fault?

This fault occurs when water is trapped inside the heat exchanger and cannot move away, causing it to overheat almost instantly. The most common reason is a failed internal circulation pump or a significant blockage in the system pipework that has stopped the flow of water entirely.

This fault often appears during the first cold spell of autumn when heating systems are switched back on after being idle all summer, which can cause internal pump components to seize.

Typical repair cost £180-450 (including labour)

DIY fix possible

Check that all radiator valves are fully open.Ensure the central heating pump is running and hasn't seized.Bleed all radiators to remove trapped air that might be blocking water flow.

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Worcester Bosch models that show the D4286 fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Worcester Bosch D4286 fault code information on this page is sourced and cross-checked against the official Worcester Bosch service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026