Low
S.8 on Vaillant ecoTEC exclusive

Your boiler is taking a mandatory cooling break to prevent overheating after a period of intense work.

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

Burner lock after heating mode

Shared across the ecoTEC exclusive range
This code is shared by the boilers in this range, which use the same control board. It may not be printed in this exact variant’s 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 code occurs when the boiler has finished a period of high-intensity heating and needs to temporarily shut down the burner to let the heat exchanger cool down. It is a protective measure to ensure the internal components don't exceed safe temperature limits. Once the internal sensors detect the temperature has dropped to a stable level, the boiler will automatically resume normal operation.

This is more common during the winter months when the boiler is running at maximum capacity for long periods to heat a cold home.

DIY fix possible

Wait up to 20 minutes for the status code to clear automaticallyEnsure radiators are turned on and TRVs are open to allow heat to dissipateCheck that the system pressure is between 1.0 and 1.5 bar on the digital display

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Avoid the next call-out bill

A cover plan would handle faults like S.8: no call-out fees, no surprise bills.

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Related fault codes

All 71 fault codes on the ecoTEC exclusive

Seeing a different code? Every code this model can display, in one place.

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