High
T.06 on Vaillant ecoTEC Plus 938

Your boiler is struggling to push water around your radiators because an external pump is not working as expected.

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

What the manual says

Manufacturer manual

External pump

From this model's manual
Verified against the Vaillant Ecotec Plus 826 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 fault occurs when the boiler detects that an additional external pump, which helps move water through your heating system, has failed or lost electrical power. The most common reason is an electrical fault in the pump itself or a break in the wiring connecting the pump to the boiler's main control board. Without this pump operating, the boiler cannot safely distribute heat, leading it to shut down to prevent overheating.

This fault is frequently seen at the start of autumn when heating systems are turned back on after months of inactivity, which can cause external pump components to seize.

Engineer required

This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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