BoilerFaultCodesYour boiler is struggling to pump water around the system, often because the water pressure is too low or there is a blockage or air bubble preventing flow.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Differential water flow switch is still open
What causes this fault?
This fault occurs when the boiler's internal sensors detect that water isn't moving through the unit quickly enough to safely carry heat away. The most common reason is that the system pressure has dropped too low, but it can also be caused by a build-up of sludge or a large air bubble trapped inside the pump. In these cases, the boiler shuts down as a safety precaution to prevent the heat exchanger from overheating.
This fault is frequently seen in autumn when heating systems are turned back on after a long summer break, as pumps can seize or air pockets can settle during periods of inactivity.
DIY fix possible
Check the pressure gauge on the front of the boiler and top it up to 1.5 bar if it is low.Ensure all radiator valves are fully open.Try bleeding your radiators to remove any trapped air.Reset the boiler to see if the fault clears.
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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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