BoilerFaultCodesYour boiler is struggling to circulate water properly or is heating up too quickly, causing it to shut down 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: System response fault
What causes this fault?
This fault occurs when the boiler detects that the water inside is heating up much faster than expected or isn't moving through the system correctly. The most common reason is a failed internal pump or a blockage, such as heavy limescale or sludge, preventing the heat from being carried away to your radiators and taps.
This fault is more frequent during the autumn when heating systems are switched back on after a long summer, as internal pump parts can become stuck through lack of use.
DIY fix possible
Check that your primary central heating valves under the boiler are fully openEnsure all radiator valves (TRVs) are turned to the maximum settingGently bleed your radiators to remove any trapped air pocketsPress the reset button once the system has cooled down
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 A02 — no call-out fees, no surprises.
Affiliate links — we may earn a commission at no extra cost to you.
Potterton Powermax HE 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.