Low
D.1 on Vaillant ecoTEC Combi

Your boiler is not broken; it is simply continuing to run the internal pump for a few minutes to safely cool down the heat exchanger after providing heating or hot 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

Water pump overrun – time for heat mode

From this model's manual
Verified against the Vaillant Ecotec 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.

What causes this fault?

This status occurs when the boiler has finished heating your radiators and needs to dissipate the high temperatures remaining inside the unit. The system keeps the internal pump running to move residual heat away from the heat exchanger and into the pipework to prevent overheating or stress on the components. This is a normal safety sequence and the boiler will automatically return to its ready state once the temperature drops.

This code is more visible during winter when the central heating is used frequently, as the pump needs to run more often to cool the system down after long periods of operation.

DIY fix possible

Wait for 5 to 10 minutesCheck if the display changes once the cooling cycle finishesEnsure your room thermostat is turned down if you want the pump to stop sooner

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