BoilerFaultCodesTechnical description
No sudden change in pressure was detected on turning on the pump: Water pressure sensor or/and pump defective, Too little water, Check adjustable bypass, Air in appliance
What causes this fault?
This fault occurs when the boiler's internal computer fails to see a small 'jump' in water pressure that should happen every time the pump starts spinning. The most common reason is that the pressure sensor has become blocked with debris or the pump itself has seized, preventing the system from confirming it is safe to ignite. It can also happen if the system pressure is simply too low for the pump to move the water effectively.
This fault often appears after the heating has been turned off for the summer, as the pump can seize up if it hasn't been used for several months.
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.