Well!......... Another update! What a palaver!!! I spoke to the fitter who put in our kitchen and did all the plumbing, and he was so helpful! He told me how to get the freezer out, which worked, and suggested we check the drip tray, electrics, and the wall as plaster, if it suffers from damp can smell like wee. So I have spent the entire afternoon squeezed into a tiny gap with a torch, cleaning out a disgusting drip tray (could they make it any harder to access?) It was below, not above the heater, so right down at floor level - difficult to see into, and to get my fingers, a cloth, cotton buds and all the other things I tried to use, in to clean it, so it took ages. AND ... there was a little mouse nest there with the mouse droppings, but luckily no mouse - he'd scarpered through a little hole he'd made in the wall, which I had to polyfilla in so he can't get back in! And the little sod had gnawed through the lead, so we need to get an electrician in to replace it. So actually, the smell could have been the mouse wee/poo, the dodgy electrical lead, or the drip tray, or a mix of all three!!! Anyway, hopefully, once the electrician has been in, everything will be fine, fingers crossed!!!