Technical Support for Hot Water Cylinders

Any traditional pumped secondary return promotes mixing which consequently destroys stratification within the hot water cylinder. Due to the lower stored temperatures achieved when using a heat pump, it is increasingly noticeable that the hot water is cooler at the taps.

Secondary hot water returns are generally used in domestic hot water applications where the point of usage (e.g. taps) is a distance away from the hot water cylinder. Known as secondary circulation, it is used to remove the need to draw off a large quantity of cool water left in the pipe run before hot water reaches the tap.

There are a couple of options available which can be used as an alternative to secondary circulation. The first is trace heating tape – this is an arrangement which reduces the temperature drop of the hot water. Trace heating tape is self-regulating and can be controlled by a time clock. A second alternative is insulation - to keep the additional energy required to maintain the hot water temperature to a minimum, all the hot water pipework needs to be well insulated.

Stratification is a term used relating to the water within a cylinder. The properties of water mean that when it is heated up, it will expand in volume (by approximately 4%) and it will become less dense. If you were able to look inside a hot water cylinder, we would see the hotter water (which is less dense) above the cooler water (more dense) and this effect is known as stratification.

Good stratification means that the majority of the cylinder contents are being warmed up to the desired temperature whereas poor stratification means that the majority of the water content is cooler.

For systems combining a solar thermal system with a heat pump or boiler, a WinterSOL kit from Grant UK can help poor stratification.

The dual thermostat fitted to a QR hot water cylinder should be set to between 50˚C and 55˚C when installed with a Grant Aerona³ air source heat pump.

When servicing a hot water cylinder, it will be necessary to drain the cylinder of its water contents – this should only be done by a competent engineer. When draining the cylinder, it is important to always switch off the heat source (such as the boiler or heat pump) and also switch off the immersion heater first. Then, you should turn off the water supply at the service valve or mains stopcock. The next step is to connect a hose pipe to the drain cock and route this pipe to a convenient gully. The drain cock can then be opened and all hot taps that are served by the cylinder should also be drained. Please note, it may take several minutes for a cylinder to empty completely.