BoilerFaultCodesYour boiler has detected that heat is not moving through the system correctly, usually meaning the water is hotter in one part of the machine than another.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Different temperature error
What causes this fault?
This fault occurs when the boiler detects a significant temperature difference between the flow and return pipes, meaning heat isn't leaving the unit fast enough. The most common reason is a lack of water circulation caused by a failing pump, a blockage in the internal pipework, or air trapped within the system.
This issue is more common in autumn when heating systems are first turned on after a long summer break, as pumps can seize during periods of inactivity.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Find a Gas Safe engineer
Search the official register for a qualified engineer in your area.
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A boiler cover plan would cover faults like E42 — 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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