Your boiler's internal control board has become too hot to operate safely and has shut down to prevent damage.

Electronic system temperature too high | Cause: Electronic system affected by external heat source, electronic fault

What causes this fault?

This fault occurs when the boiler's main control board reaches an unsafe temperature, forcing the system to shut down to prevent the electronics from melting or catching fire. The most common reason is an internal part becoming too hot due to a failing heat shield or a component on the circuit board itself short-circuiting and generating excessive heat.