BoilerFaultCodesWhat the manual says
Manufacturer manualWater shortage, temperature difference between flow and return NTC too large
What causes this fault?
This fault occurs when the boiler detects that water isn't circulating through the pipes and radiators fast enough to carry heat away from the burner. The most common reasons are a seized internal pump or a blockage in the system, such as a buildup of sludge or a clogged heating filter, which prevents the water from moving freely. Because the heat cannot escape, the boiler reaches a dangerous temperature and shuts down to prevent internal damage.
This fault is frequently seen at the start of autumn when the heating is turned on for the first time after summer, as the pump can seize during long periods of inactivity.
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 F.23: no call-out fees, no surprise bills.
Affiliate links. We may earn a commission at no extra cost to you.