Medium
d.88 on Vaillant ecoTEC sustain

Your boiler is struggling to detect the flow of water needed to start heating your hot water tap, likely due to a sensor issue or a drop in water pressure.

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

Flow rate limit value for ignition in domestic hot water mode

From this model's manual
Verified against the Vaillant Ecotec Sustain installation & service manual, page 49.
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.

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