BoilerFaultCodesYour boiler is heating up too quickly because water isn't moving through the system properly, causing it to shut down to prevent overheating.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Dry fire protection (temperature gradient of flow NTC too steep) | .Air in boiler/system, pump blocked or defective, pump output too low
What causes this fault?
This fault occurs when the internal sensors detect that the water inside the boiler is getting hot far too quickly, which usually means the water isn't flowing away from the heat exchanger. The most common reason is a failing pump that can't push the water around, though it can also be caused by a large air bubble trapped in the pipework blocking the path.
This issue often appears at the start of autumn when the heating is turned on for the first time after summer, as pumps can seize up during long periods of inactivity.
DIY fix possible
Check that all radiator valves and isolation valves are fully openBleed your radiators to remove any trapped air from the systemEnsure the boiler pressure is between 1.0 and 1.5 bar on the pressure gauge
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 F.24 — no call-out fees, no surprises.
Affiliate links — we may earn a commission at no extra cost to you.
Vaillant Thermocompact 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.