BoilerFaultCodesTechnical description
Overheating protection on primary heat exchanger triggered | Cable or cable connection of fuse in the primary heat exchanger defective, or primary heat exchanger defective
What causes this fault?
This fault occurs when a dedicated safety fuse inside the boiler melts because the main heat exchanger has reached a dangerously high temperature. It is usually caused by a lack of water flow, a severe internal blockage, or the buildup of debris that prevents the system from cooling itself down properly. This is a critical safety shutdown designed to prevent the metal components from warping or cracking.
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.
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