BoilerFaultCodesWhat the manual says
Manufacturer manualTemperature 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.
Engineer required
This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
Avoid the next call-out bill
A cover plan would handle faults like b30: no call-out fees, no surprise bills.
Affiliate links. We may earn a commission at no extra cost to you.