BoilerFaultCodesYour boiler is overheating because water is not moving through the system quickly enough to carry the heat away.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Primary flow temperature rising too fast
What causes this fault?
This fault occurs when the water inside the boiler heats up much faster than the system can pump it away. It is usually caused by a failing pump that isn't pushing water effectively or a internal blockage, such as sludge or limescale, that is restricting the flow. When the sensors detect this rapid heat spike, the boiler shuts down to prevent internal damage or melting.
This issue often surfaces during the first cold snap of autumn when a pump that has been idle all summer has seized or 'stuck' and cannot restart.
DIY fix possible
Ensure all radiator valves (TRVs) are turned to their highest settingCheck that the boiler pressure is between 1 and 1.5 bar on the gaugeSwitch the electricity to the boiler off and back on again to reset the system
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 D4341 — no call-out fees, no surprises.
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Worcester Bosch CDi Classic 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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