BoilerFaultCodesYour boiler has detected an unusual temperature difference between its sensors and has shut down to prevent any internal damage.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Sensor control protection activation
What causes this fault?
This fault occurs when the boiler detects a conflicting temperature reading between its internal flow and return pipes. It usually happens because water isn't moving through the unit fast enough, or because one of the temperature sensors has become inaccurate or faulty. The boiler shuts down as a safety measure to prevent the heat exchanger from overheating due to this poor circulation.
This fault is more frequent in winter when heating systems are under high demand, as sludge or debris in the radiators can more easily restrict the water flow required for the boiler to operate safely.
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.
Gas Safe Register →Protect yourself from future repair bills
A boiler cover plan would cover faults like A42 — no call-out fees, no surprises.
Affiliate links — we may earn a commission at no extra cost to you.
Ferroli Bluehelix Tech 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.
Affiliate links — we may earn a commission at no extra cost to you.