Your boiler is displaying a status reading for the warm start sensor temperature rather than an error, which is part of the system's normal operational monitoring.

Current temperature for warm stat sensor

What causes this fault?

This code appears because the boiler is communicating its current internal temperature reading for the warm start function rather than an actual error. It physically occurs when the system is monitoring the thermal store to ensure instant hot water is available. You are seeing a live status update of the sensor's data, which means the internal computer is working exactly as intended.