BoilerFaultCodesYour boiler is heating up too quickly because water isn't flowing 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: Water shortage (Temperature rise too fast)
What causes this fault?
This fault occurs when the boiler's internal sensors detect that the water temperature is rising much faster than it can be carried away into your radiators. The most common reason is a failed or stuck circulation pump, which stops the water from moving through the pipes. It can also be caused by a heavy buildup of sludge or debris blocking the heat exchanger, or simply because there is air trapped in the system.
This fault is frequently seen in autumn when heating systems are switched back on after being idle all summer, which can cause the internal pump to seize.
DIY fix possible
Check if your system pressure is between 1 and 1.5 bar and top up if lowEnsure all radiator valves and isolation valves are fully openBleed your radiators to remove any trapped air pockets
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 ecoMAX Pro 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.