BoilerFaultCodesTechnical description
Fault: Flow/return sensor - Temperature difference between flow and return temperature sensor is too great
What causes this fault?
This fault occurs when the boiler's internal computer notices that the flow and return pipes have wildly different temperatures, which shouldn't happen during normal operation. The most common reason is that one of the temperature sensors has become faulty or uncalibrated, though it can also be caused by a physical blockage or a pump failure preventing water from circulating correctly.
This fault often surfaces when the heating is first turned on after summer, as internal components like the pump can seize or debris can settle 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.