BoilerFaultCodesYour boiler has sensed that heat is rising too quickly because there is likely not enough water circulating through the pipes.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: waiting time: no water in system, temperature (gradient error) rise flow / return sensor too high
What causes this fault?
This fault occurs when the boiler detects an unusually rapid rise in heat that cannot be carried away from the heat exchanger quickly enough. The most common reason is a lack of water flow, often caused by a failing internal pump, a physical blockage in the pipework, or air trapped within the system. Essentially, the boiler is shutting down to prevent itself from overheating because the heated water has nowhere to go.
This issue often surfaces at the start of autumn when heating systems are turned back on after being idle, which can cause internal pump parts to seize.
DIY fix possible
Check the pressure gauge on the boiler or under the sink; it should be between 1 and 1.5 barIf pressure is low, use the filling loop handles to top up the system with water until it reaches the green zoneEnsure all radiator valves and the isolation valves under the boiler are fully open
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 S.54 — no call-out fees, no surprises.
Affiliate links — we may earn a commission at no extra cost to you.
Glow-worm Flexicom cx 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.