BoilerFaultCodesYour boiler has likely overheated because water isn't moving through the pipes correctly or there is too much trapped air in the system.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Heating sensor damaged, no water circulation or air in system
What causes this fault?
This fault occurs when the boiler's internal temperature exceeds a safe limit, causing the system to shut down for safety. The most common reasons are a pump that has failed or seized, a blockage in the heat exchanger, or a significant buildup of air that prevents water from absorbing heat properly.
This issue is more frequent in autumn when the heating is turned back on after months of inactivity, as circulation pumps are prone to seizing during the summer break.
DIY fix possible
Check that your system pressure is between 1 and 1.5 barBleed your radiators to remove any trapped airEnsure all radiator valves and isolation valves are fully openReset the boiler using the reset button
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 A03 — no call-out fees, no surprises.
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Could it be time for a new boiler?
If repair costs are adding up, a new energy-efficient boiler could be the smarter long-term choice.
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