BoilerFaultCodesTechnical description
Overheating protection on – primary heat exchanger has responded
What causes this fault?
This fault occurs when a dedicated safety fuse inside the main heat exchanger melts because the component has reached an unsafe temperature. The most common reason is a buildup of limescale or sludge that restricts water flow, causing the metal to overheat and permanently blow the fuse. Unlike a standard overheat, this is a one-time safety device that cannot be simply reset.
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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