BoilerFaultCodesYour boiler has detected that water is not moving through the system correctly, causing a temperature imbalance that has shut the unit down for safety.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Maximum difference failure between 2 NTC temperature sensor – poor circulation.
What causes this fault?
This fault occurs when the boiler's internal sensors detect that water is heating up too quickly or not flowing away from the heat exchanger fast enough. The most common reasons are a failed or blocked circulation pump, air trapped in the system, or a buildup of sludge and debris that has restricted the internal pipework. Because the heat cannot be moved into your radiators effectively, the boiler shuts down to prevent the unit from overheating.
This issue is most frequently seen at the start of autumn when the heating is turned back on after being idle all summer, which can cause the internal pump to seize.
DIY fix possible
Check that your boiler pressure is between 1.0 and 1.5 bar on the gauge.Ensure all radiator valves and isolation valves under the boiler are fully open.Gently bleed your radiators to remove any trapped air pockets.Reset the boiler by pressing the 'R' or Reset button.
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A boiler cover plan would cover faults like E17 — no call-out fees, no surprises.
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Could it be time for a new boiler?
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