BoilerFaultCodesYour boiler has stopped running because the water inside it has become hotter than the temperature you have requested.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: Current primary water temperature higher than set value
What causes this fault?
This fault occurs when water is staying inside the boiler's heat exchanger for too long, causing it to overheat beyond the safe limit. The most common reasons are a pump failure that prevents water from moving around your radiators, or a blockage such as trapped air or sludge that is restricting the flow. Because the heat cannot be carried away from the boiler quickly enough, the system shuts down as a safety precaution.
This issue is more common during the first cold spell of autumn, when pumps that have sat idle all summer can seize up or struggle to restart.
DIY fix possible
Check that your radiator valves are open to allow water to circulateEnsure there is no air trapped in your radiators by bleeding themCheck that the boiler pressure gauge is between 1 and 1.5 barReset the boiler to see if the fault clears
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 204 O — 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.