BoilerFaultCodesYour boiler has switched itself off because it has detected it is getting too hot, likely due to a circulation problem or a temporary blockage.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: The boiler is fitted with a safety thermostat to protect against overheating of the water. If this thermostat operates the boiler will lockout.
What causes this fault?
This fault occurs when the water inside the boiler reaches an unsafe temperature, triggering a safety switch to prevent damage. The most common reason is a failure in the internal pump preventing water from moving away from the burner, or a build-up of sludge and debris creating a blockage in the heat exchanger.
This issue often surfaces during the first cold spell of autumn when the heating system is turned back on after being idle all summer, which can cause internal pump components to seize.
DIY fix possible
Check that your radiator valves are open and not turned to zero.Ensure your system pressure is between 1 and 1.5 bar on the gauge.Turn the selector switch to the reset position for five seconds, then turn it back to the 'on' position.
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 Lockout (Red) light flashing once a second — no call-out fees, no surprises.
Affiliate links — we may earn a commission at no extra cost to you.
Potterton Performa SL HE 9 2 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.