BoilerFaultCodesWhat the manual says
Manufacturer manualExcessive temperature rise
What causes this fault?
This fault occurs when the heat inside the boiler builds up much faster than the water can carry it away. The most common reason is a blockage or a failing pump preventing the water from flowing through the pipes and radiators effectively. It can also be caused by a build-up of sludge or debris inside the main heat exchanger, which restricts the water path.
This fault is frequently seen at the start of autumn when heating systems are turned back on after being idle all summer, which can cause internal pump parts 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 b25: no call-out fees, no surprise bills.
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