High
A1 on Worcester Bosch Greenstar CDi Compact

Your boiler is struggling to move water because there is air trapped in the system or the water pressure has dropped too low.

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

Controlled characteristic pump has run dry

From this model's manual
Verified against the Worcester Bosch Greenstar Cdi Compact installation & service manual.
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 boiler detects that there is no water passing through the internal pump, causing it to spin without resistance. The most common reasons are a significant drop in system pressure or a large pocket of air becoming trapped inside the pump itself, which prevents it from being able to circulate heat. To protect the internal components from overheating or burning out, the boiler triggers a safety shutdown.

This issue is frequently seen in autumn when heating systems are turned back on after the summer, as air often settles in the pump or radiators during 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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