BoilerFaultCodesYour boiler has detected that there is not enough water circulating through the system, which could be due to a leak or a mechanical issue with the pump.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Water is leaking or the pump needs replacing or freeing due to the pump running dry.
What causes this fault?
This fault occurs when the boiler detects a serious lack of water pressure or circulation, often caused by a leak within the system or a failing internal pump. If the pump is spinning without enough water (running dry) or has become seized with debris, the boiler will shut down to prevent the components from overheating or burning out. In some cases, a faulty air vent can also cause an air lock that tricks the sensors into thinking the system is empty.
This issue is frequently seen in autumn when heating systems are switched back on after a long summer break, as pumps are more likely to seize if they haven't been used for several 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 A1 — no call-out fees, no surprises.
Affiliate links — we may earn a commission at no extra cost to you.
Worcester Bosch CDi Classic 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.