Thanks Samuri, got it, job done ! Hidden in plain sight : Annoyingly inlet and outlet pipes aren’t push fit , seemed to be glued in to the tank so had to just unscrew it and drop in a bucket of hot water, which worked. I should have thought of the tank , similar to freestanding water coolers, but I guess I discounted that as I didn’t see where there was space but of course it’s elongated and flat against the back wall. Just need to see if the problem reoccurs but I’ve bumped the temp from 3c up to 4c and just need to make sure I run off some water each day. Thanks again.