Medium Lockout
S.41 on Vaillant ecoTEC Pro / ecoTEC Plus

Your boiler has too much water in the system, causing the pressure to rise to a level that is higher than recommended for safe operation.

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

Water pressure > 2.8 bar

What causes this fault?

This fault occurs when the water pressure inside your system rises to an unsafe level, usually because the filling loop has been left slightly open or or is leaking water into the system. It can also happen if the internal expansion vessel, which manages water pressure as it heats up, has failed or lost its air charge. In some cases, a faulty plate heat exchanger may be allowing fresh mains water to leak into the central heating circuit.

DIY fix possible

Check that the filling loop valves are fully closedBleed a radiator from the top valve to release excess waterMonitor the pressure gauge until it returns to between 1.0 and 1.5 barReset the boiler if the code does not clear automatically

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