High
338 on Worcester Bosch Greenstar CDi Compact

Your boiler has repeatedly tried to start but failed to detect water movement, so it has locked itself out to prevent internal damage.

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

Too many short burner starts without confirmation Reset button There is an error where the pump is not detecting water.

From this model's manual
Verified against the Worcester Bosch Greenstar Cdi Compact installation & service manual, page 66.
Plain-English guidance below. Severity, DIY steps, costs and parts are our interpretation to help you act, not text from the manual.

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 →
Boiler cover options

Avoid the next call-out bill

A cover plan would handle faults like 338: 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 guides you might find useful

Banging / kettling / whistling noise

Each noise points to a different fault.

Read →

No hot water but heating works

Almost always a stuck diverter valve on combis.

Read →

Radiators cold at the bottom

Sludge build-up — needs flushing, not bleeding.

Read →