Mira [J] fault codewhat it means and how to fix it

The relay board is the part of an electric shower that does the heavy work. The control electronics decide how much heat is wanted; the relay board is what physically closes contacts to put mains across the heating elements, and it handles the full current the appliance draws. That is a demanding job — tens of amps, switched repeatedly, in a warm damp enclosure — and it is why the relay board is one of the components that genuinely wears out rather than merely failing at random.

Code J is Mira reporting that this board is no longer working correctly, and their published action is a single line: contact customer services. There is nothing an owner can do with this one and no sequence that clears it. What is worth understanding is where it sits relative to the other board fault in this table. A cover PCB failure, code H, is the user-interface side — the electronics behind the front panel that read the button and drive the lights.

A relay board failure is the power side. They fail differently and cost differently, and telling them apart depends entirely on the second Status reading, because the initial indication does not distinguish them. It is also worth knowing what a relay board failure does not mean. It is not a safety fault in the sense the tripping and burning-smell pages are — the appliance has detected an internal problem and stopped, which is the system behaving correctly. The reason it is rated caution rather than information is that a board switching that much current is not something to keep power-cycling in the hope it comes back.