BoilerFaultCodesTechnical description
When the Flue Gas Temperature > 80°C for 5s, the Slave board shuts down
What causes this fault?
This fault occurs when the internal heat exchanger is failing to transfer heat effectively into the water, causing it to escape through the flue instead. The most common reasons are a heavy buildup of debris inside the heat exchanger or a lack of water flow, which prevents the system from cooling down properly. In some cases, it may simply be a faulty sensor incorrectly reporting that the exhaust is overheating.
This issue often surfaces during the first cold snap of winter when the boiler is forced to run at maximum capacity for long periods, putting more stress on the heat exchanger.
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.