BoilerFaultCodesYour boiler is overheating because the water inside is heating up too quickly, causing the system to shut down temporarily for safety.
Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.
Technical description: The display shows alternatively the CH flow temperature and E9. The gradient limitation is active. The primary temperature is rising too fast and the burner has switched off for 2 minutes. See error E9.
What causes this fault?
This fault occurs when the water inside the boiler heats up at an abnormally fast rate, suggesting that the heat isn't being moved away from the burner quickly enough. The most common reasons are a failing pump that cannot circulate the water or a physical blockage, such as limescale or sludge, trapped within the main heat exchanger.
This fault often appears in autumn when the heating is turned back on for the first time, as pumps can seize up after being idle during the summer months.
DIY fix possible
Check that your boiler pressure gauge is between 1 and 1.5 barEnsure all radiator valves are fully open particularly the lockshield valvesInspect the condensate pipe for signs of freezing if the weather is very cold
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 E9 — 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.