If you want to serve multiple sinks or locate the heater out-of-sight, e.g. beneath a sink, you will need a mains pressure storage water heater (sometimes called an unvented water heater). You can install the heater more or less anywhere, but because the tank pressurised at the incoming cold mains pressure you will need to fit a safety relief valve and possibly other accessories if there is a cold water drinking supply nearby. This makes installation a little more complex, but overall we believe these heaters offer a much better solution than either instant or oversink water heaters. They are our best selling range of water heating products.
These units are typically mounted directly under a sink, although because the units operate at mains pressure the location of the heater is a purely a matter of convenience. Whilst the specific details may vary from product to product, some features of this type of product are generic as outlined below:
These units use electric heating elements rated at 3kW or less and may be wired to a domestic ring main. The electrical power requirements are similar to a typical electric kettle -- there is normally no need to connect directly to the electrical consumer unit.
The water supply connection is made by tee-ing from the cold water mains. It is recommended that a service valve is also fitted at the time of installation to facilitate future maintenance or re-siting of the unit.
A useful benefit of these water heaters is that they are suitable for operation with regular taps, proving high mains pressure flow rates for both hot and cold water outlets. (Please note that the alternative vented class of undersink water heater requires the use of special vented taps which can be expensive to purchase if not already available).
Unvented water heaters can supply a number of sinks, with the practical limitation often being determined by capacity of the water storage unit.
Depending on on the specific details of the installation, unvented water heaters may require accessories to be fitted to the cold inlet pipework. The requirements may include an external safety pressure relief valve and may also include a small expansion vessel plus check valve to accommodate expansion of water during the heating process, and a pressure reducing valve if the local water mains pressure is unusually high. These accessories are similar across the range of unvented water heaters and are a requirement of UK regulations for capacities over 15 litres.
This guide provides a high level guide to the general features of products in this range. Installation details vary between products. All installations must be carried out in accordance with the manufacturer's specific requirements and with relevant regulations. Installation must always be carried out by competent persons.Close