Installation Requirements; Thesystem - Potterton Housewarmer 45 Installation & Service Instructions Manual

3. Installation Requirements – Page 6
3.1 The System
The boiler must be used on INDIRECT hot water systems
only. It is suitable for use on open vented gravity domestic
hot water/pumped central heating systems or, fully pumped
systems which may be sealed or open vented.
The system should be designed so that the maximum static
head does not exceed 30.5m (100ft) and a minimum on fully
pumped systems of 0.9m (3ft). See Fig. 5.
Gravity domestic hot water circuits should have a minimum
circulating head of 1.2m (4ft). See Fig. 4.
To prevent reverse circulation in the gravity circuit when the
pump is running an injector tee is provided - See Fig.14. The
orientation of the tee is not important.
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.
Combined Gravity Hot Water Pumped Central Heating
Systems.
Where a cylinder thermostat and zone valve is used to
control the temperature of the hot water it is recommended
that a by-pass be installed in the gravity circuit. A suggested
method of doing this is shown in Fig. 4. where the bathroom
radiator is connected into the gravity circuit and is fitted with
two lockshield valves. Mechanically operated thermostatic
domestic hot water temperature control valves which allow
the boiler to operate when the valve is closed or partially
closed MUST NOT BE FITTED.
Note: Flow connections can be fitted to either upper
tappings, return connections to either of the lower tappings.
When not using the Injector Tee, the flow and return
connections must be fitted on the same side.
Fully Pumped Systems
We recommend that if possible the pump be wired directly to
the terminal block (See Fig. 17) 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 shut down thus
preventing nuisance operation of the overheat thermostat.
If the pump is not wired directly to the terminal block, then a
by-pass circuit is not necessary.
If a three port diverter valve is used as shown in Figs.5 & 6,
a by-pass is not necessary since one circuit is always open.
Where a pair of two port valves are used, a by-pass is
necessary. It should be fitted with a lockshield valve and be
adjusted to maintain a minimum flow through the boiler of
4.5 litres/min (1 gal/min) see Figs. 5 & 6.
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 1kW (3,400 Btu/h)
2. Maintaining a minimum water flow through the boiler
of 9 litres/min (2 gal/min).
A suggested method of meeting these requirements by using
a bathroom radiator fitted with two lockshield valves is
shown in Figs. 5 & 6.
Diagrammatic layouts of a fully pumped system and a
combined pumped central heating/gravity hot water system
are shown in Figs. 4 & 5.
Sealed Systems (Fully Pumped)
Installation
The installation must comply with the requirements of BS
6798; 1987 and BS5449: Pt 1. 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 BS4814: Pt 1. shall
be fitted close to the inlet side of the pump. 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).