BoilerFaultCodesYour boiler is struggling to circulate water properly, often because the system pressure is too low or there is trapped air preventing the heat from moving away from the boiler.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Water level low Temperature range too wide | Cause: Pump obstructed, pump running at lower capacity, Air in appliance, system pressure too low, flow and backflow NTC reversed
What causes this fault?
This fault occurs when the boiler detects a massive temperature difference between the water going out to your radiators and the water coming back, suggesting the heat isn't moving. The most common reasons are that the system doesn't have enough water pressure to move or there is a large pocket of air trapped inside the internal pump. In some cases, the pump itself has reached the end of its life and can no longer push the water around your home effectively.
This fault often appears in autumn when the heating is turned on for the first time after summer, as pump components can seize during long periods of inactivity.
DIY fix possible
Check the pressure gauge and top up to 1.5 bar using the filling loop if it is too lowBleed your radiators to remove any trapped air from the systemEnsure all radiator valves are fully open and not stuck
Find a Gas Safe engineer
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A boiler cover plan would cover faults like F.23 — no call-out fees, no surprises.
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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.
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