BoilerFaultCodesYour boiler has detected that water is heating up too quickly or not circulating properly through the system, 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: Temperature differential exceeded
What causes this fault?
This fault occurs when the water inside the boiler heats up much faster than the system can carry it away, suggesting a major flow restriction. The most common reasons are a failed pump that isn't pushing the water around or a blockage caused by a buildup of sludge and debris in the main heat exchanger. In some cases, air trapped in the system or closed valves can also prevent the necessary circulation.
This issue is more common in autumn when heating systems are switched back on after being idle all summer, which can cause internal pump components to seize.
DIY fix possible
Check that all radiator valves are fully openEnsure your boiler pressure is between 1.0 and 1.5 barBleed all radiators to remove trapped air pockets
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 b30 — no call-out fees, no surprises.
Affiliate links — we may earn a commission at no extra cost to you.
Vokera Pinnacle 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.