What is a thermal store and how does it work?

How a thermal store works

A thermal store is a cylinder that holds hot primary water, the same water that circulates through your radiators, rather than the water that comes out of your taps. In an Advance Appliances thermal store that water is kept at around 75°C by the boiler or other heat source.

Cold water from the mains runs through a heat exchanger coil inside the store. It picks up heat on the way through and goes on to your taps and showers at mains pressure. A blending valve, set at 50°C and adjustable, mixes in cold water so the hot water arrives at a steady, safe temperature.

The water you wash with is never held in the tank. That is why most Advance models can give mains pressure hot water while the store itself stays open vented at atmospheric pressure.

The stored water also heats your radiators

The same bank of hot water feeds the central heating. It acts as a buffer between the boiler and the radiators, which gives fast radiator heat-up and helps the boiler work efficiently.

Types of thermal store

• Direct (single coil) stores, such as the TSD and TSDC, are heated straight from the boiler water and use two pumps: one for the boiler and one for the heating.
• Indirect (twin coil) stores, such as the TSi and TSiC, have a coil for the boiler, so they work with Y plan, S plan and W plan systems and need only one pump.
• Electric thermal stores, such as the ECO ETS, are heated by two 3kW immersion heaters, designed to run on a low tariff supply.
• Multi fuel thermal stores, such as the SFUTS, link several heat sources, including wood burners and solar.

The TSD and TSi have a feed and expansion tank built in. The TSDC and TSiC are cylinder only, for homes that already have a feed and expansion tank and want to keep it.

Boilers can heat a thermal store; heat pumps need a different cylinder

Advance's standard thermal stores are designed for gas, oil, LPG, solid fuel and biomass boilers. They are not designed to run on a heat pump alone, because the store works at 75°C, which is hotter than a heat pump normally supplies. For a heat pump, a heat pump cylinder is the right choice.

Standards and guarantee

Advance thermal stores are made from stainless steel and meet the Hot Water Association Thermal Store Specification and Parts G and L of the Building Regulations, according to the Advance standard thermal store installation guide. Advance is a Hot Water Association charter member. The store is guaranteed for ten years and the fitted components for two.

One householder, Peter F from St Albans, wrote in a customer review: "The thermal store is going strong after ten years with no signs of failing in any department." See the full thermal store range.