My Elson Coral water heater has been replaced by an unvented hot water storage unit by Gledhill with a 180 litre capacity. My plumber has been looking after the Elson Coral for 3 years but in March I noticed it was leaking. It subsequently turned out that the foam insulating material inside the casing was saturated with water – no visible cracks so it was leaking via the joints. My plumber was quoted £1,500 for a new Elson Coral tank (plus labour charges). The Gledhill was about £800 (plus labour charges). The door frame of the cupboard has to be removed to get the tank out so its not an easy option and needs 2 people because of the weight of the it.
This tank is stainless steel and is similar in construction to a vacuum flask. It can only be installed by a suitably qualified plumber and has to have an annual maintenance check. There is a helpful explanation on a website run by MODUS called 'Guide to mains pressure unvented water heating'.
The new tank has not been in long enough for me to do any cost comparison. What I have noticed is that the water is much hotter so I don't use so much. The insulation is much better as there is no 'warmth' in the cupboard now. And it doesn't make any noise when the electricity comes on.
Hope this helps.