BoilerFaultCodesTechnical description
Primary flow switch not operated or requires investigation.
What causes this fault?
This fault occurs when the boiler's internal sensors do not detect enough water movement to operate safely, usually because the pump has failed or the flow switch is stuck. The most common reason is that the rubber diaphragm inside the flow valve has perished or the pump has become seized after a period of inactivity.
This issue often appears in early autumn when the heating is turned on for the first time after summer, as the pump can seize during the warmer 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.
Find a Gas Safe engineer
Search the official register →