Current Water Regulations and Byelaws permit unvented water heaters with capacity of 15 litres or less to accommodate the expansion of the water that occurs during the heating cycle in the system pipe work. To achieve this the pipe work between the nearest cold water draw off and the water heater must be of sufficient volume to accommodate the expansion.
If it is not possible to accommodate the expansion in the system pipe work, it is then necessary to use an expansion vessel and non return valve (KIT A).
If the mains water pressure may exceed 3.5 bar a pressure reducing valve (KIT B) should also be installed.
The discharge from relief valves must be made in a safe and conspicuous manner; therefore a tundish (KIT C) is available for 10 and 15 litre units if required.