22
clean heat technology
The factory set pre-charge pressure is suitable for systems with a static head of up to 5
metres. If the static head is greater than 5 metres then the pre-charge pressure of the
expansion vessel will need to be increased. Increase the pressure using a standard car
tyre pump and pressure gauge when the system is empty (zero pressure).
Normally expansion requirement is 4% of the system water content including the Boiler.
IMPORTANT
The 10l Expansion vessel supplied with the Boiler is suitable for systems
requiring a maximum expansion of 9 litres.
For systems requiring more expansion a second expansion vessel will be
required. BS7074 Part 1 includes information on this requirement.
5-5.4 Pressure Relief Valve
A pressure relief valve (PRV) is supplied with the ‘system boiler kit’.
The PRV must be fitted to the flow pipe from the Boiler. It MUST be the first fitting in the
flow pipe and MUST be adjacent to the Boiler.
The PRV will vent excess pressure from the system. The valve will open when the
pressure exceeds 3 Bar ± 10%.
The pressure relief valve can be manually opened by turning the red knob clockwise, to
close the valve continue turning clockwise until it clicks.
5-5.5 Pressure Relief Valve Discharge Pipe
The outlet from the pressure relief valve must be piped using 15mm copper pipe to a
visible position outside the dwelling by the installer. The pipe must have a continuous fall
and ideally be terminated over a drain.
Local by-laws may require a Tundish to be fitted.
5-5.6 Pressure Gauge
A pressure gauge is supplied in the ‘system boiler kit’, idealy this should be fitted to the
PRV unit, however it can be fitted anywhere in the system.
When the system is full with cold water and all radiators are full, on and vented, the gauge
will show the cold fill pressure. Set the red pointer to the cold fill pressure. If the system
pressure, indicated by the black pointer, falls below the cold fill pressure, it indicates that
the system requires topping up.
5-5.7 Cold Fill Pressure
The Cold Fill Pressure of the central heating system should be:-
Recommended Pressure - 2 Bar Max. Pressure - 3 Bar Min. Pressure - 1 Bar
5-5.8 Filling Loop
A Filling Loop comprising a flexible hose, double check valve and an isolating valve is
supplied with the system boiler kit for filling and topping up the system - see 5-5g.
The filling loop should be fitted between the incoming mains and the heating system return
as shown in fig. 5-5a or 5-5b. Locating the filling loop within site of the PRV and pressure
gauge is recommended, however it can be fitted elsewhere but an extra gauge must be
fitted adjacent to the filling loop.
The take off from the main for the filling loop must be after any pressure reducing valve
and before the water softener, if fitted.
When not in use one of the hose unions must be disconnected as there must not be a
permanent connection to the mains supply.
INST
INST
INST
INST
INSTALLA
ALLA
ALLA
ALLA
ALLATION 5
TION 5
TION 5
TION 5
TION 5
IMPORTANT
Scalding water and steam can be blown
out of the discharge pipe. Position the
discharge so that it is not a hazard to
property or people (especially children).
0
1
2
3
4
5
6
0
20
40
60
80
bar
psi
Fig. 5-5e PRV and Gauge
HEATING
FLOW
PRV DISCHARGE
Fig. 5-5f Gauge
Note
For accurate setting
of the pre-charge
pressure a digital
pressure gauge is
recommended.
Fig. 5-5d Static Head
HIGHEST POINT OF SYSTEM
EXPANSION VESSEL
STATIC HEAD
55555
