High
d3 on Worcester Bosch 537i

Your boiler has lost the signal from an external control, such as a thermostat or heating timer, meaning it cannot receive the command to turn on.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

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.

What the manual says

Manufacturer manual

Jumper 8-9 not detected.

From this model's manual
Verified against the Worcester Bosch 537i installation & service manual, page 46.
Plain-English guidance below. Severity, DIY steps, costs and parts are our interpretation to help you act, not text from the manual.

What causes this fault?

This fault occurs when the water inside the boiler reaches an unsafe temperature, causing the safety switch to trip and shut everything down to prevent damage. The most common reasons are a failed pump that isn't moving hot water away from the heat exchanger quickly enough, or a blockage within the system pipework.

This fault is more common when the heating is first turned on after summer, as circulation pumps can seize up after long periods of inactivity.

Engineer required

This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Related fault codes

d1View →d2View →

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