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26
IMPORTANT GENERAL CHECKS
15.9
DOMESTIC HOT WATER (DHW) MODE
15.9.1 Fully open all DHW taps in turn and ensure that water flows freely from them.
15.9.2
Close all taps except the furthest one from the boiler and check that the boiler is firing at maximum rate.
This is factory set to give a DHW temperature rise of approximately 35°C at the flow rate stated Section
5 Technical Data.
15.9.3
Reduce the DHW draw-off rate to about 3l/min and check that the boiler modulates to deliver DHW at
approximately 60°C.
15.9.4 Close the DHW tap and check that the main burner extinguishes. The pump should
overrun for 60 seconds.
NOTE:
On systems in excess of 2 bar inlet pressure a water pressure governor may be required
to prevent water noise.
15.10
CENTRAL HEATING (CH) & DOMESTIC HOT WATER (DHW) MODE
15.10.1 Ensure that the CH external controls are calling for heat. The burner should light. Display
should read 58°C.
15.10.2 Fully open a DHW tap and check that hot water is delivered. Display should read 58°C.
15.10.3 Gas
Rate
:
Check the boiler gas rate when the boiler is at full DHW output.
Check at the gas meter, with no other appliance in use. Refer to Tables 1 & 2 for gas rates.
15.10.4 Close the DHW tap. The burner should go off and the pump continue to run.
15.10.5 Set the central heating external controls to OFF. The burner should go off and the pump continue to run
until the CH return temperature falls below 35°C.
15.10.6 Check the correct operation of the timer (if fitted) and all other system controls. Operate each control
separately and check that the main burner responds.
15.11
FLUSHING THE SYSTEM & WATER CIRCULATION
15.11.1 With the system HOT, examine all water connections for tightness. The system pressure will increase with
temperature rise but should not exceed 2.5 bar.
15.11.2 With the system still hot, turn off the gas, water and electricity supplies to the boiler and drain down to
complete the flushing process.
NOTE:
A flushing solution should be used during the flushing procedure. Flushing solutions: Fernox Superfloc,
Sentinel X300 (new systems) or X400 (existing systems).
15.11.3 Refill and vent the system, add inhibitor, clear all air locks and again check for water tightness.
15.11.4 With the system COLD, check that the initial pressure is correct to the system design requirements. For
pre-pressurised systems, this should be 1.0 bar.
15.11.5 Reset the system initial pressure to the design requirement.
15.12
BALANCE THE SYSTEM
15.12.1
The boiler does not normally need a bypass but at least some radiators on the heating circuit, off load at
least 10% of the minimum boiler output, these must be provided with twin lockshield valves so that the
minimum heating load is always available. See paragraph 6.1.10 regarding thermostatic radiator valves.
NOTE:
Systems incorporating zone valves which could completely cut off the flow through the system must also
include a bypass.
15.12.2 BALANCING
a. Set the programmer to ON.
Close the manual or thermostatic valves on all radiators, leaving the twin lockshield valves (on the
radiators referred to above) in the open position.
Turn up the room thermostat and adjust the lockshield valve to give an uninterrupted flow through
the radiator.
These valves should now be left as set.
b. Open all manual or thermostatic radiator valves and adjust the lockshield valves on the remaining
radiators, to give around 20°C temperature drop at each radiator.
c. Adjust the room thermostat and programmer to normal settings.
15.12.3 Check the condensate drain for leaks and check that it is discharging correctly.
15.12.4 Finally, set the controls to the User’s requirements.
NOTE:
The pump will operate briefly as a self-check once
every 24 hours in the absence of any system demand.
15.13 WATER
TEMPERATURES
Temperatures can be selected using the CH and DHW
thermostats.
FIGURE 29.
FIGURE 28.
TABLE. 6
Button
Setting
CH Flow
Temperature
DHW Outlet
Temperature
Max
80°C
60°C
Min
45°C
40°C
