When I moved into my new house I was aching all over from carrying heavy boxes and wanted a nice hot bath. I turn the hot tap and the hot water trickles out, no power behind it. The house has a weird thermal store thing rather than the conventional hot water tank so I decided to call the company that made them. They determined asap that it was out of guarantee and referred me to a plumber. I called him and he said that it was probably because the heat exchanger was scaled up and needed changing.
I called him round and he said that the thermal stores were being put in a lot of new houses in my area which was a mistake because the water is very hard and they scale up very quickly. The thermal store relies on keeping a supply of very hot water inside, about 85 degrees C. When someone turns on a tap a heat exchanger uses the hot water to heat up cold mains water to 60 degrees very rapidly, giving instant hot water at mains pressure. Nice in theory but he reckons that 85 degrees makes the pipes scale up quicker. Our house is only two years old.
He replaced the heat exchanger for £250 and gave me a quote for £850 for a water softener or £1600 to rip out the thermal store and put something better in. I am more tempted by the water softener idea since we would get all the advantages of a water softener: soap lasting longer (!), no limescale marks on the shower cubicles, no furry elements, life would be heavenly.
I haven't given the nod yet, I ought to get more quotes.
With the new heat exchanger the thermal store is wonderful: nice powerful hot shower, even on the top floor. It can fill a basin with hot water in seconds. Turning the central heating on, the house is warm in minutes where my old house took hours.
The plumber was very cynical about the thermal store, he seemed to hate them. I am wondering whether he is right or whether he only ever sees the ones that aren't working and he doesn't particularly enjoy fixing them?
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Peter's Moblog
It's a solid and valid technology, but often treated with suspicion by many plumbers. Installed correctly with a little thought (like putting in a water softner in hard water areas) it should serve you well. The only thing "better" to replace it with would be a mains pressure unvented cylinder which is like a traditional cylinder but run at high pressure. They work well but plumbers like them as they need to have an annual service - circa £50...
The heat exchanger could probably have been easily descaled too rather than replaced.