BoilerFaultCodesTechnical description
Water shortage, temperature difference between flow and return NTC too large. Pump blocked or defective, pump output too low, flow and return NTC interchanged
What causes this fault?
This fault occurs when water is leaving the boiler much hotter than when it returns, which suggests the water isn't moving through your radiators quickly enough. The most common reasons are a failing internal pump that can't push the water effectively or a blockage caused by a buildup of sludge and debris in the pipework.
This fault is more frequent in autumn when the heating is turned on for the first time after summer, as pump components can seize or sludge can settle during 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.