Table of Contents
Advertisement
Pre-Installation
4.4
Minimum volume and execution of the heating
system
Normally the energy for the defrost cycle is drawn form the buffer
cylinder and the heating system, but in small systems with low flow the
controller may switch to draw energy from the DHW cylinder instead.
Even the electrical heater may be activated to ensure a proper defrost.
4.5
Check size of expansion vessel (central heating side)
Characteristic diagram for expansion vessel
Safety valve
3.0
setting (bar)
Vessel charge
0.5
and initial
system
pressure
(bar)
Total water
Select an expansion vessel with a nominal volume not
content of
less than given below (litres)
system
(litres)
25
2.1
50
4.2
75
6.3
100
8.3
125
10.4
150
12.5
175
14.6
200
16.7
225
18.7
250
20.8
275
22.9
300
25.0
Multiplying
0.0833
factors for
other system
volumes
Table 7 Capacities of expansion vessel
14
1.0
1.5
2.7
3.9
5.4
7.8
8.2
11.7
10.9
15.6
13.6
19.5
16.3
23.4
19.1
27.3
21.8
31.2
24.5
35.1
27.2
39.0
30.0
42.9
32.7
46.8
0.109
0.156
4.6
Pressure relief pipework
CAUTION
Scalding risk from hot water or steam!
▶ The pressure relief valve (PRV) and temperature & pressure relief
valve (TPRV) are appliance safety devices and may discharge hot
water or steam when activated.
▶ The outlet pipe should be sited in such a way that it does not cause a
hazard or an obstruction when discharging, for example above a
window, entrance door or other public access way.
▶ The point of termination should provide a visual indicator in case the
PRV/TPRV discharges.
• The pressure relief discharge pipe [1 or 3] should be run in pipe
which has a diameter of at least 15mm, that is made of copper or a
material that will withstand PRV/TPRV discharge temperatures and
pressures, and which complies with BS 5254 or BS EN 1451.
• Plastic pipework must be properly supported with a maximum of
300mm between supports to prevent sagging.
• The PRV discharge pipe must run continuously downwards away from
the appliance to a safe point of discharge.
• The pressure relief should discharge away from any electrical or other
hazard, preferably to an external drain or soak-away.
• The pipe [1 or 3] should be finished with a partial bend, to face the
external wall (as shown) to ensure safe discharge of hot water.
• In all normal circumstances a PRV discharge pipe installation as
described above sufficiently meets all but the most exceptional
circumstances.
– Where the PRV discharge pipe could be susceptible to damage,
vandalism, freezing etc that could cause either a blockage or
restriction in the ability to discharge safely then a tundish should
be considered. The tundish should be sited in a position where
damage to the property or injury to occupants cannot occur from
any spillage or discharge.
1
2
3
4
Fig. 15 Pressure relief pipework
[1]
Discharge pipe (turned back onto external wall example)
[2]
Outside wall
[3]
Discharge pipe (into drain or gully example)
[4]
External drain
Pre plumbed cylinder – 6 721 852 928 (2023/04)
1
2
2
3
4
Advertisement
Table of Contents
