BoilerFaultCodesWhat the manual says
Manufacturer manualThe rate of temperature rise measured by the heating flow thermistor is too high.
What causes this fault?
This fault occurs when the water inside the boiler gets hot too quickly because it isn't moving away from the heat source fast enough. The most common reasons are a pump that has failed or become stuck, or a blockage within the main heat exchanger that is restricting water flow.
This issue is more frequent in autumn or winter when the heating is first turned on after a long summer break, as pumps can often seize up from lack of use.
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 25: no call-out fees, no surprise bills.
Affiliate links. We may earn a commission at no extra cost to you.