BoilerFaultCodesYour boiler has detected that the water pressure is too low or water is not flowing correctly through the system to operate safely.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: CH water system pressure low, automatic air vent closed, or primary flow valve diaphragm damaged (Section C)
What causes this fault?
This fault occurs when the boiler's internal sensor detects that water is not moving through the heat exchanger at the required speed or pressure. The most common reasons are a lack of overall system pressure or a physical failure of the rubber diaphragm inside the flow valve, which prevents the boiler from safely firing up. It can also be caused by trapped air pockets or a pump that is no longer pushing water effectively.
This issue is frequently seen in autumn when heating systems are turned back on after a summer of inactivity, as internal moving parts can seize or stick.
DIY fix possible
Check the pressure gauge on the front of the boiler; it should be between 1 and 1.5 bar.If the pressure is low, use the external filling loop valves to top up the system until the needle reaches 1.2 bar.Ensure the black cap on the automatic air vent inside the boiler is slightly loose to allow air to escape.Restart the boiler to see if the flashing light clears.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
Gas Safe Register →Protect yourself from future repair bills
A boiler cover plan would cover faults like Primary flow switch operated neon flashing — no call-out fees, no surprises.
Affiliate links — we may earn a commission at no extra cost to you.
Potterton Performa System E is discontinued — time for a new one?
Parts for discontinued models can be hard to find and expensive. A new A-rated boiler could save you money on both repairs and energy bills.
Affiliate links — we may earn a commission at no extra cost to you.