Inside rear panel bulging
Unplug the unit and take out all the drawers and remove the back (behind the drawers) panel carefully. (This back panel has foamy thermal insulation behind it and this will be probably be enmeshed with ice - you may have to wait awhile for this ice to melt before you can remove the panel, even after you have unscrewed it.When you have got the back panel off, you will see a large solid block of ice, probably halfway up the cooling coils, right down to the bottom of the exposed space. You have to melt all this ice (I used a hair dryer to blow warm air onto the ice (have towels and a bucket ready to mop up the melted water, otherwise it will run over the floor. When you have melted all this ice, you will see a drain hole at the bottom of the exposed space. This will have ice in it and it must be cleared. Then replace the back panel and all should be OK. The panel bulges because ice/water is accumulating behind the panel, water, when it freezes, expands, forcing the panel forwards.I reckon it's a Hotpoint Design fault. What is supposed to happen is that during the heating cycle, melted ice drops down from the cooling coils and down the drain hole onto a plate over the compressor unit, where it evaporates. BUT, during the cooling cycle, a fan circulates cold air from the cooling coils, through the entire unit, which includes the chamber behind the panel that is below the coils. Thus this chamber gets cold (-18 deg.C) so that water dripping down during the heating cycle is frozen before it has a chance to fall down the drain hole.I now defrost in this manner every six months or so. Sadly, very sadly, Hotpoint, like other white goods manufacturers (Baxi Potterton boilers for instance) do not reply to my enquiries.Hope this helps.