DORCHESTER DR-FC 25, Installation, Commissioning And Maintenance Instructions

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Functioning of the water heater
14 Instruction Manual DR-FC
2
gis
Tabel 2.2 shows the trip point per water heater.
n
Remark
The trip point of the pressure switch is not adjustable.
2.4.5 Flame probe
To ensure that no gas will flow when there is no combustion, an flame probe has
been fitted. The control panel uses this rod for flame detection, by means of
ionisation detection. The control panel cuts in, the instant it detects that there is
a gas flow but no flame.
2.5 Safety of the instal-
lation
2.5.1 Unvented installation
With an unvented installation, a expansion valve and expansion vessel prevent
excessive pressure in the heater. This prevents damage being caused to the
enamelled coating (in the water heater) or to the heater. A non-return valve
prevents excessive pressure in the water supply system. This valve also
prevents water from flowing backwards from the heater into the cold water
supply system. The pressure reducing valve protects the installation against an
excessively high water supply pressure. These components are fitted to the cold
water pipe. See paragraph
’3.6.1 Cold water side’ .
2.5.2 Vented installation
With a vented installation, excess pressure is taken up by the open water tank.
The level of the water tank determines the maximum working pressure in the
heater, which may not exceed 8 bar. The installation must also be fitted with an
open vent from the hot water pipe. Ideally the vent pipe should be linked to a
separate tundish/drain or else to the cold water storage tank. A safety valve
should also be fitted to the water heater. See paragraph
’3.6.3 Hot water side’ .
2.5.3 T&P valve
A T&P valve is mandatory in an ’unvented’ installation.
A T&P valve monitors the water pressure in the water heater and the water
temperature at the top of it. If the pressure in the water heater becomes
excessive (> 7 bar) or the water temperature is too high (>97°C), the valve will
open. The hot water will immediately flow out of the heater. Because the water
Tabel 2.2 Pressure switch trip points
Water
heater Pressure differential
[Pa]
Closing Opening
DR-FC
25
> 635 < 605
DR-FC
30
> 855 < 825
DR-FC
45
> 885 < 855
DR-FC
60
> 1085 < 1055