BoilerFaultCodesYour boiler has shut down because a safety sensor has detected that it is getting far too hot, likely due to a blockage or a pump failure.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Maximal flue gas thermostat or heat exchanger maximal thermostat has activated
What causes this fault?
This fault occurs when the water inside the boiler reaches an unsafe temperature or the flue gases become too hot, triggering a safety shut-off to prevent damage. The most common reasons are a failed internal pump that isn't moving water away quickly enough or a blockage in the system from sludge and debris. It can also be caused by an air lock or a closed valve stopping the flow of water through the heat exchanger.
This fault is more common in autumn when heating systems are switched back on after a long summer break, as pumps are prone to seizing 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.
Gas Safe Register →Protect yourself from future repair bills
A boiler cover plan would cover faults like 224 — no call-out fees, no surprises.
Affiliate links — we may earn a commission at no extra cost to you.
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.
Affiliate links — we may earn a commission at no extra cost to you.