Section 6: Sealed Systems
Page 19
up to 3 bar. Radiator valves must comply with the requirements of BS
2767:1991.
One or more drain taps (to BS 2879) must be used to allow the
system to be completely drained.
6.2 Filling the Sealed System
Filling of the system must be carried out in a manner approved by the
local Water Undertaking.
Only ever fill or add water to the system when it is cold and the
boiler is off. Do not overfill.
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WaRninG
The procedure for filling the sealed system is as follows:
1. Check the air charge pressure in the expansion vessel BEFORE
filling the system.
The expansion vessel charge pressure should always be slightly
greater than the maximum static head of the system, in bar, at
the level of the vessel (1 bar = 10.2 metres of water). Refer to
Figure 6-1.
The charge pressure must not be less than the actual static head
at the point of connection.
the air charge pressure may be checked using a tyre pressure
gauge on the expansion vessel Schraeder valve. the vessel
may be re-pressurised, when necessary, using a suitable
pump. When checking the air pressure, the water in the heating
system must be cold and the system pressure reduced to zero.
nOtE
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Check that the small cap (or screw) on all automatic air vents is
open at least one turn. The cap (or screw) remains in this position
from now on.
2. Open the hinged hopper lid. Undo the two screws (one on the
right and one on the left) and remove the access cover from the
top of the boiler.
Pull out the air vent tube so that it will discharge any water
outside the boiler and have a small container available to catch
this water. Open the manual air vent located under the access
cover. Refer to Figure 6-2.
3. Ensure that the flexible filling loop is connected and that the
double check shut off valve connecting it to the water supply is
closed. A valve is open when the operating lever is in line with the
valve, and closed when it is at right angles to it.
4. Open the fill point valve.
5. Gradually open the double check valve from the water supply
until water is heard to flow.
6. When the needle of the pressure gauge is between 0.5 and 1.0
bar, close the valve.
7. Vent each radiator in turn, starting with the lowest one in the
system, to remove air.
8. Continue to fill the system until the pressure gauge indicates
between 0.5 and 1.0 bar. Close the fill point valve. The system fill
pressure (cold) should be 0.2 - 0.3 bar greater than the vessel
charge pressure – giving typical system fill pressures of approx
0.5 bar for a bungalow and 1.0 bar for a two storey house.
Refer to the Domestic Heating Design Guide for further
information if required.
9. Repeat steps 7 and 8 as required until system is full of water at
the correct pressure and vented.
10. Water may be released from the system by manually operating
the safety valve until the system design pressure is obtained
11. Close the fill point and double check valves either side of the
filling loop and disconnect the loop.
12. Check the system for water soundness, rectifying where
necessary.
6.3 Venting the Pump
For those heating circulating pumps fitted with a vent plug, it is
important that the pump is properly vented to avoid an air lock and
also prevent it running dry and damaging the bearings.
Unscrew and remove the plug from the centre of the pump motor.
Using a suitable screwdriver, rotate the pump spindle about one turn.
Replace the plug in the motor. Do not over tighten.
Some heating circulating pumps are not fitted with a
vent plug so it is not possible to vent these pumps in the
manner described above. Refer to pump manufacturers own
instructions for further details.
nOtE
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6.4 Pressure Relief (Safety) Valve Operation
Check the operation of the pressure relief (safety) valve as follows:
1. Turning the head of the valve anticlockwise until it clicks. The
click is the safety valve head lifting off its seat allowing water to
escape from the system.
2. Check that the water is escaping from the system.
3. Top-up the system pressure, as necessary.
Figure 6-2:
Location of manual air vent (wash system removed for
clarity)
