Thermal store
cylinders explained.
A thermal store looks like a hot water cylinder but works the other way round. Here is how it works, how it compares with an unvented cylinder, and your options if it needs replacing.
How a thermal store works
In a normal cylinder, the stored water is the water that comes out of your taps. In a thermal store, the stored water is heating water. Your mains cold water passes through a coil (a heat exchanger) inside the store and is heated on its way to the taps.
Because the taps are fed directly from the mains, a thermal store gives mains-pressure hot water, similar to a combi boiler or unvented cylinder.
Thermal store or unvented cylinder?
- A thermal store does not hold hot water under pressure, so it does not need the same safety valves or an annual unvented check
- An unvented cylinder usually gives a stronger flow to several taps at once
- Thermal stores often work with more than one heat source, such as a boiler and solar, or a wood burner
- Hot water flow from a thermal store depends on the coil size and the store temperature
Common problems
- Hot water that runs cool quickly
- Limescale in the mains coil reducing the flow
- Pump or valve faults on the heating side
- Leaks from the store or its tank in the loft, on some models
We can assess a thermal store and repair it, or price a replacement.
Replacing a thermal store
A thermal store can be replaced like for like, or with an unvented cylinder heated by your boiler. Changing to an unvented cylinder needs a good mains supply and a discharge pipe route, and is priced at a free survey.
See unvented cylinders or our online cylinder price.