Medium Lockout
D.75 on Vaillant ecoTEC

Your boiler is taking longer than expected to heat up your hot water tank, causing the system to stop as a precaution.

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.

Technical description

Maximum charging time for a storage without own controller

What causes this fault?

This fault happens when the boiler fails to heat your hot water cylinder within a set time limit, usually because the internal sensors haven't detected a sufficient rise in temperature. The most common cause is a faulty sensor giving an incorrect reading, or a mechanical failure in the diverter valve which prevents heat from actually reaching the water tank.

DIY fix possible

Check that the valves on your hot water cylinder are fully openEnsure your thermostat is calling for hot waterTry resetting the boiler to see if the error clears

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Related fault codes

F.22View →F.24View →S.24View →

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