BoilerFaultCodesYour boiler has sensed that the temperature is rising too quickly or unevenly, which usually means water isn't flowing through the system as it should.
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 between T1 and T2 exceeded
What causes this fault?
This fault occurs when the heat generated by the burner cannot be carried away from the heat exchanger quickly enough, leading to a rapid heat spike. The most common reason is a failed circulation pump or a blockage in the system, such as sludge or debris, which prevents the water from moving. It can also be caused by a faulty sensor giving an incorrect temperature reading to the boiler's computer.
This issue often appears when the heating is first turned on after summer, as pump components can seize during long periods of inactivity.
DIY fix possible
Check that your radiator valves are openEnsure the boiler pressure is between 1 and 1.5 bar on the gaugeGently bleed your radiators to remove any trapped air
Find a Gas Safe engineer
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A boiler cover plan would cover faults like 430 — no call-out fees, no surprises.
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Ideal Response SE 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.
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