Medium
3 flashes on Worcester Bosch Greenstar 25CDi

Your boiler's hot water temperature sensor has stopped working, which means the system cannot accurately heat your water.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Book a service

This fault should be looked at by a Gas Safe engineer within the next week or two. It may get worse if left.

What the manual says

Manufacturer manual

Hot water NTC sensor defective. Check hot water NTC sensor and connecting lead for circuit breaks/short circuits.

From this model's manual
Verified against the Worcester Bosch/Worcester Bosch Greenstar 25cdi 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.

Engineer required

This fault requires 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 3 flashes: 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.

All 21 fault codes on the Greenstar 25CDi

Seeing a different code? Every code this model can display, in one place.

2 flashes4 flashes5 flashes6 flashes7 flashes8 flashes9 flashesA7b1C6CH flow NTC sensor defective.Code plug not detected.E2E9F7Fan speed too low.Flame not detected.Internal error.Rapid flashesSlow flashes

Related guides you might find useful

No hot water but heating works

Almost always a stuck diverter valve on combis.

Read →

Yellow or orange flame — CO safety

Safety-critical — turn off, read this.

Read →

Is boiler cover worth it?

Break-even maths on monthly cover.

Read →