Just in case anyone else gets this error. It turns out my unit had been incorrectly assembled at the factory. Wrong tempsensor leads had been used and the input and exhaust connections transposed.
This meant the supply from atmosphere was read as the exhaust from dwelling, in the cold spell this meant the unit saw the room as being below 5c and so shut unit down.
Before stripping unit down tech support diagnosed a faulty sensor , so i bought a sensor and patch kit. Once stripped down error became apparent. They also sent me a copy of the exploded parts diagram and circuit board connections that for some reason don’t appear in the supplied documentation.
Well over a day wasted , but they did say sorry.