Low
5 pulses / No light on Worcester Bosch Greenstar i Junior

Your boiler has been accidentally switched into a specific testing mode used by engineers, rather than having a mechanical breakdown.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Monitor it

This is a minor fault. Keep an eye on it and mention it at your next annual boiler service. Reset the boiler and see if it clears.

What the manual says

Manufacturer manual

Not a fault code. Service mode selected to max, press service button to return to normal.

From this model's manual
Verified against the Worcester Bosch Greenstar I Junior 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.

DIY fix possible

Locate the blue 'Service' button on the front control panel.Press and hold the 'Service' button for several seconds.Wait for the indicator light to stop flashing and return to its standard display mode.

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 5 pulses / No light: 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

Is boiler cover worth it?

Break-even maths on monthly cover.

Read →

When to replace your boiler

7 signs repair isn't worth it anymore.

Read →

New boiler cost 2026

Realistic UK prices for a swap.

Read →