Table of Contents
Advertisement
1.6
The System
If plastic pipe is used for the central heating circuit there
must be a run of at least 1m of uninsulated copper pipe
from the boiler flow and return connections.
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.
Before installing a new boiler to an existing system treat
the system with an appropriate descaling/flushing agent
as per the instructions supplied with the treatment
package. It is recommended that any corrosion inhibitors
and descalers/flushing agents used are manufactured
by Fernox or BetzDearborn
The system should be designed so that the maximum
static head does not exceed 30.5 m and there is a
minimum on fully pumped systems of 300 mm. See Fig.
9.
Gravity domestic hot water circuits should have a
minimum circulating head of 1.2 m. See Fig. 8.
Horizontal pipe runs should be kept to a minimum. To
prevent reverse circulation in the gravity circuit when the
pump is running an injector tee is incorporated.
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. A drain
point is also provided on the heat exchanger should the
boiler need draining - see Fig. 22.
Combined Gravity Hot Water Pumped Central
Heating Systems.
It is recommended that a cylinder thermostat and zone
valve are used to control the temperature of the hot
water and that a by-pass be installed in the gravity
circuit. A suggested method of doing this is shown in Fig.
8. 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 UNLESS a bypass radiator is
fitted. Note: The boiler has one flow and two return
connections. On combined gravity DHW/Pumped central
heating a Tee will be needed in the flow which must be
fitted directly to the connecting pipe provided.
Publication No. 5102977
Fully Pumped Systems
The pump must be wired directly to the terminal block
(See Fig. 20) 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 a three port diverter valve is used as shown in Figs.9 &
10, 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. 9
& 10.
Systems fitted with controls which allow the boiler to
operate when both the hot water and central heating
circuits
are
closed
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. 9 & 10.
Diagrammatic layouts of a fully pumped system and a
combined pumped central heating/gravity hot water
system are shown in Figs. 8 & 9.
Sealed Systems (Fully Pumped)
Installation
The installation must comply with the requirements of BS
6798: 1987 and BS 5449: 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/in
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/in
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.
i.e.
mechanically
operated
2
) shall be used. It must comply
2
) shall be fitted to
Installation Requirements
11
Hide quick links:
Advertisement
Table of Contents
