High
Over temperature on Worcester Bosch Greenstar 25Si

Your boiler has reached an unsafe temperature and has automatically shut down to prevent damage and ensure your safety.

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

Primary temperature 94°C (until 84°C) - shut down burner. Water over 89°C - shut-down. Gas valve OFF.

From this model's manual
Verified against the Worcester Bosch Greenstar 25si 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 water inside the boiler cannot flow away quickly enough, causing it to rapidly overheat and trigger a safety shutdown. The most common reasons are a seized internal pump that isn't pushing water around the system, or a blockage such as trapped air or a build-up of sludge. In some cases, a faulty sensor may simply be misreading the temperature even if the water itself is fine.

This issue often appears when the heating is first turned on after summer, as the pump can seize up during 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.

Find a Gas Safe engineer
Search the official register →

Avoid the next call-out bill

A cover plan would handle faults like Over temperature: no call-out fees, no surprise bills.

Approved partner
Domestic Appliance Guard
Unlimited call-outs, 24/7 helpline, no price-hike promise
Get a quote →

Affiliate links. We may earn a commission at no extra cost to you.

Related fault codes

Related guides you might find useful