BoilerFaultCodesTechnical description
Water shortage, temperature difference between flow and return sensors too large
What causes this fault?
This fault occurs when the water inside your boiler heats up too quickly because it isn't moving around the system fast enough. The most common reason is a failing pump that can no longer push the water through the pipes, or a blockage in the heat exchanger that is restricting flow. When the boiler detects such a large temperature difference between the water going out and the water coming back, it shuts down to prevent internal damage.
This issue often comes to light during the first cold spell of autumn, when a pump that has been idle all summer has seized up or struggled to restart.
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.