Low
S.23 on Vaillant ecoFIT Pure 412

Your boiler is currently in the process of starting up to heat your water, which is a normal part of its routine operation.

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

Hot water handling mode: Burner ignition

From this model's manual
Verified against the Vaillant Ecofit Pure 412 installation & service manual, page 28.
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

Wait a few minutes to see if the boiler successfully finishes its ignition cycle and proceeds to normal operation.If the code persists for more than 15 minutes, turn the boiler off at the fused spur for 30 seconds and switch it back on to force a restart.

Find a Gas Safe engineer
Search the official register →
Boiler cover options

Avoid the next call-out bill

Monthly cover means no unexpected bills when your boiler breaks down.

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

S.20View →S.21View →F.28View →

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 →