BoilerFaultCodesYour boiler has detected that water is not circulating correctly through the system, often due to a pump issue or a blockage.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Primary flow fault
What causes this fault?
This fault occurs when the boiler's internal sensors detect that water isn't moving through the heat exchanger as quickly as it should, causing a sudden spike in temperature. The most common reasons are a failed or sticking circulation pump, a buildup of sludge blocking the pipes, or air trapped within the system preventing flow.
This code is frequently seen when heating is first turned on in autumn, as pumps can seize up after being left idle throughout the summer months.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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 E154 — no call-out fees, no surprises.
Affiliate links — we may earn a commission at no extra cost to you.
Baxi GA Range 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.