BoilerFaultCodesYour boiler has stopped working because it cannot detect water moving through the internal pipes to keep the system safe.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: No Water Flow
What causes this fault?
This fault occurs when the boiler's internal sensors do not detect enough water movement to safely heat the system, causing it to shut down to prevent overheating. The most common reasons are a failed circulation pump that can no longer push water through the pipes, or a blockage caused by a build-up of debris and sludge. It can also be triggered if the water pressure is too low or if air is trapped inside the heat exchanger.
This fault often appears when the heating is first turned on in autumn, as pumps can seize up after sitting idle throughout the summer months.
DIY fix possible
Check the pressure gauge on the front of the boiler is between 1 and 1.5 barIf the pressure is low, use the filling loop underneath the boiler to top it upEnsure all radiator valves and isolation valves under the boiler are fully openPress the Restart button to clear the fault
Find a Gas Safe engineer
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Gas Safe Register →Protect yourself from future repair bills
A boiler cover plan would cover faults like 4.12 — no call-out fees, no surprises.
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Could it be time for a new boiler?
If repair costs are adding up, a new energy-efficient boiler could be the smarter long-term choice.
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