Section 4: Sealed System Page 19
Pressure Gauge
The pressure gauge must have an operating range of 0 to 4 bar.
It must be located in an accessible place next to the filling loop for the system.
Safety Valve
The safety valve (provided with the heat pump) is set to operate at 3 bar. It
should be fitted in the flow pipework near to the heat pump. The safety valve
should be connected to a discharge pipe which will allow the discharge to
be seen, but cannot cause injury to persons or damage to property.
Filling Loop
Provision should be made to replace water lost from the system. This can
be done manually (where allowed by the local water undertaking) using
an approved filling loop arrangement incorporating a double check valve
assembly.
The filling loop must be isolated and disconnected after filling the system.
Heating System
The maximum ‘setpoint’ temperature for the central heating water is 55°C.
An automatic air vent should be fitted to the highest point of the system.
If thermostatic radiator valves are fitted to all radiators, a system by-pass must
be fitted. The by-pass must be an automatic type and correctly set when the
system is commissioned.
All fittings used in the system must be able to withstand pressures 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.
4.2 Filling the Sealed System
Filling of the system must be carried out in a manner approved by the local
Water Undertaking.
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 approximately
0.2 bar lower than the maximum static head of the system, at the level
of the vessel (1 bar = 10.2 metres of water).
Refer to Figure 4-1.
The charge pressure must not be less than the actual static
head at the point of connection.
2. 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 until filling is
completed and then it is closed.
3. Remove the top (6kW) and front right (10kW and 13 & 17kW) casing
and loosen the plug on the automatic air vent located inside the heat
pump. Refer to Figure 4-3.
loosen
tighten
Auto air vent
Plug
Figure 4-3: Auto Air Vent
4. 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.
5. Open the fill point valve.
6. Gradually open the double check valve from the water supply until
water is heard to flow.
7. When the needle of the pressure gauge is between 0.5 and 1.0 bar,
close the valve.
8. Vent each radiator in turn, starting with the lowest one in the system, to
remove air.
9. 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.
10. Repeat steps 8 and 9 as required until system is full of water at the
correct pressure and vented.
11 . Water may be released from the system by manually operating the
safety valve until the system design pressure is obtained.
12. Close the fill point and double check valves either side of the filling loop
and disconnect the loop.
13. Check the system for water soundness, rectifying where
necessary.
14.
4.3 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.
WARNING
Only ever fill or add water to the system when
it is cold and the heat pump is off. Do not
overfill.
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.
The expansion vessel air pressure, system
pressure and operation of the pressure relief
valve must be checked on each service. Refer
to Section 10.
NOTE
NOTE
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