Thermal store work in a different way to conventional cylinders in that the water that goes through the coil is the water that comes out your taps. They are similar to unvented cylinders in that they work on mains pressure but are not governed by the requirement of a G3 qualification.
The body of water inside the cylinder is also pushed around the heating system. Thermal stores are traditionally found in flats where the temperature and pressure relief pipe may not be able to be routed to outside.
At Transgas Services we can undertake the repair, service or installation of thermal stores and can offer the best advice/solution for your needs.