The System - Potterton Osprey CF 125 Installation & Service Instructions Manual

Installation Requirements - Page 9

1.6 The System

When installing the boiler on an existing system, the system
should be chemically cleaned prior to installation.
The boiler must be used on INDIRECT hot water systems
only. It is suitable for use only on fully pumped systems
which may be sealed or open vented.
The system should be designed so that the maximum static
head does not exceed 30m and a minimum of 500mm. See
Fig. 6.
The pump should preferably be fitted in the flow, though
installation in the return is acceptable providing care is taken
to ensure air is not drawn into the system due to the
negative pressure effects of the pump. Isolating valves must
be fitted as close as possible to allow replacement without
system draining.
Drain off taps should be fitted in the pipework close to the
boiler and in the low points of the system.
Fully Pumped Systems
The pump must be wired directly to the terminal block
(See Fig. 12) as it will allow the pump to be controlled by
the over-run device. This will ensure that the pump will
continue to run after boiler shuts down thus preventing
nuisance operation of the overheat thermostat.
Systems fitted with controls which allow the boiler to
operate when both the hot water and central heating
circuits are closed i.e. mechanically operated
thermostatic control valves, must be fitted with a by-pass
circuit capable of:-
1. Dissipating a minimum of 2kW.
2. Maintaining a minimum water flow through the boiler
of 8 L/min.
A suggested method of meeting these requirements by
using a bathroom radiator fitted with two lockshield
valves is shown in Figs. 6 & 7.
Diagrammatic layouts of a fully pumped open system
and a fully pumped sealed system are shown in Figs. 6
& 7. The central heating should be designed as such
that the minimum flow through the boiler is above 8
L/min.
Sealed Systems (Fully Pumped)
Installation
The installation must comply with the requirements of
BS 6798: 1987 and BS 5449: 1990. The British Gas
publication "British Gas Specification for Domestic Wet
Central Heating Systems" should also be consulted.
Safety Valve
A non-adjustable spring-loaded safety valve, preset to
operate at 3 bar (45lbf/in2) shall be used. It must
comply with BS 6759: Pt 1. and include a manual
testing device. It shall be positioned in the flow pipe
either horizontally or vertically upwards and close to the
boiler. No shut-off valves are to be placed between the
boiler and the safety valve. The valve should be
installed into a discharge pipe which permits the safe
discharge of steam and hot water such that no hazard
to persons or damage to electrical components is
caused.
Pressure Gauge
A pressure gauge incorporating a fill pressure indicator,
covering the range 0 - 4 bar (60 lbf/in2) shall be fitted to
the system. It should be connected to the system,
preferably at the same point as the expansion vessel.
Its location should be visible from the filling point.
Expansion Vessel
A diaphragm type expansion vessel to BS 4814: Pt 1.
shall be fitted close to the inlet side of the pump on the
flow from the boiler before any valves. The connecting
pipework should not be less than 15mm. Pipework
connecting the expansion vessel should not incorporate
valves of any sort. Methods of supporting the vessel
are supplied by the vessel manufacturer. The nitrogen
or air charge pressure of the expansion vessel shall not
be less than the hydrostatic head, (height of the top
point of the system above the expansion vessel).