Low
S.28 on Vaillant ecoTEC Pro / ecoTEC Plus

Your boiler is taking a short, programmed break to prevent the burner from starting and stopping too frequently while heating your water.

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 burner anti-cycling time

From this model's manual
Verified against the Vaillant Ecotec Combi installation & service manual, page 43.
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 status occurs when your boiler reaches its target temperature too quickly and needs to pause to prevent the internal components from wearing out. It is the boiler's way of protecting itself from 'short-cycling,' which usually happens because the heat has nowhere to go or the water is already at the desired temperature. Once the internal timer finishes and the water has cooled slightly, the boiler will fire up again automatically.

This is more common during the autumn and spring when your heating is turned on but the outdoor temperature is mild, meaning the boiler doesn't need to run for long to reach the required heat level.

DIY fix possible

Wait for 5 to 10 minutes for the countdown to finishEnsure hot water taps are fully closedCheck that the pre-heat (Comfort mode) is not set too high

Find a Gas Safe engineer
Search the official register →

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

Related guides you might find useful