BoilerFaultCodesTechnical description
Flow return sensor temperature test
What causes this fault?
This fault occurs when the boiler's internal sensors detect that water isn't moving through the heat exchanger as quickly as it should, leading to a rapid heat build-up. The most common reasons are a failing circulation pump that can't push the water around or a blockage in the system, such as a build-up of sludge. It can also be triggered if the temperature sensors themselves have become faulty and are sending incorrect data to the control board.
This issue often comes to light during the first cold snap of autumn when the heating is 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.