Your boiler has detected that the exhaust gases are getting too hot, which has caused the system to shut down for safety.

High fume temperature – the exchanger probe detects an excessive temperature

What causes this fault?

This fault occurs when the internal sensors detect that the gases leaving your boiler are significantly hotter than they should be, triggering an automatic shutdown to prevent damage. The most common reason is a buildup of limescale or debris inside the heat exchanger which prevents heat from being transferred to your water, or a faulty sensor giving an incorrect reading.