BSS Audio BOSS 100, Installation & Maintenance Manual, Page: 12 / 48

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Prior to connecting the expansion vessel to the system the pipework should be flushed and tested.
When the vessel is connected the system should be pressurised when cold. If the initial system water
pressure is too high, the diaphragm will be displaced too far into the vessel. This will leave the vessel
unable to accommodate the volume of expansion water. The result of this is an increase in system
pressure and the safety valve will lift.
Primary Coil Connections
Connect the primary connections (Indirect only). The primary circuit must be positively pumped. Either
primary connection may be used as the primary flow. Reheat times are identical either way. The primary
circuit can be open vented or sealed, with up to a maximum pressure of 3.5 bar. If you seal the primary
circuit an additional expansion vessel and safety valve is required.
The boiler may be Gas, Electric or Oil but must be under effective thermostatic control. Uncontrolled
heat sources such as some AGA’s, back boilers, solid fuel stoves, etc. are not suitable. Please contact
our Technical department for guidance. Connect the two port zone valve (indirect only) into the primary
flow pipework. The direction of flow arrow should be towards the primary flow connection.
Installing The Two Port Motorised Valve
The function of the Two Port Motorised Valve prevents the cylinder from overheating. It can be installed
on either horizontal or vertical pipework.
If it is mounted onto horizontal pipework the valve head must face upwards. The direction of flow is
marked on the body of the valve with arrows.
Thermostatic Mixer
When installing a solar system with an unvented BSS BOSS™ twin coil cylinder, a thermostatic mixing
valve should be installed. Its function is to act as an anti-scald protection. The thermostatic mixer is
to be set to a temperature of between 30°C and 60°C and is supplied by the installer.
Secondary Circulation
On larger installations long pipe runs to draw-off points can cause significant volumes of water to be
drawn off before an acceptable temperature can be reached. Secondary pumped circulation using
a stainless steel or a bronze pump, and combined with effective time and temperature controls can
overcome this problem. Where secondary return circulation is required the pipework should be run in
15mm pipe. A suitable WRAS approved stainless steel or bronze circulation pump must be used. A
check valve must also be installed to prevent back flow.
On large secondary circulation systems it may be necessary to incorporate an extra expansion vessel
into the circuit to accommodate the increased system water volume. Secondary circulation should be
avoided on Direct electrically heated units being used on off-peak electricity tariffs. It should be noted
that the use of a secondary circulation circuit can increase running costs as there will be circulation pipe
losses. High levels of insulation on secondary pipework are required to keep energy losses to a minimum.