High Lockout
E78 on Potterton Promax HE

Your boiler's internal sensor is struggling to accurately read the water pressure, which prevents the system from operating safely.

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.

Technical description

Water pressure sensor fault

What causes this fault?

This fault occurs when the boiler's internal electronic sensor can no longer accurately monitor the water pressure inside the system. The most common reason is that the sensor has suffered an electrical failure or has become blocked by debris and sludge build-up, preventing it from sending a reliable signal to the main control board.

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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