BoilerFaultCodesTechnical description
Heat exchanger temperature limiter or flue gas temperature limiter has tripped. or Flue pipe is blocked.
What causes this fault?
This fault occurs when the water inside the boiler gets too hot or the exhaust gases exceed safe limits, triggering a safety shutdown to prevent damage. The most common reasons are a lack of water circulation caused by a failed pump, a blockage in the heat exchanger, or a buildup of air or sludge in the system. Essentially, the heat being generated isn't being moved away quickly enough, causing the unit to overheat.
This issue often surfaces during the first cold spell of autumn when the heating is turned back on after being idle all summer, which can cause internal pump components to seize.
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.