DORCHESTER DR-LA 110, Руководство пользователя

Страница: 14 / 64

Functioning of the water heater
14 Instruction manual DR-LA
2
gis
2.4.2 Combustion products discharge safety device
The flue gases are channelled to the outside via the draught diverter
b
and the
flue gas discharge
a
. To prevent the flue gases from flowing back into the boiler
room, the discharge ducting is monitored by a feature called the combustion
products discharge safety device. This uses a flue gas thermostat
f
with flue
gas thermostat sensor
g
which are located in the draught diverter. Under
normal circumstances this sensor will register the ambient temperature.
However, if the chimney is not drawing sufficiently (for example, due to a
blockage in the chimney), the flue gases will flow back past the flue gas
thermostat sensor. The sensor will then detect an excessive temperature and
the flue gas thermostat will open. The heat demand will be ended and the burner
control immediately stops the heating cycle. The flue gas thermostat will also
lock out. This must be manually reset, before the water heater can be put back
into operation.
2.4.3 flame probe
To ensure that no gas can flow when there is no combustion, an flame probe
A
has been fitted. The burner control uses this rod for flame detection, by means
of ionisation sensing. The burner control closes the gas valve as soon it detects
that gas is flowing and there is no flame.
2.5 Safety of the instal-
lation
2.5.1 Unvented installation
With an unvented installation, an expension valve and expansion vessel prevent
excessive pressure in the water heather. This prevents damage of the water
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 regulates the water
supply pressure to a normal operating pressure of 3.5 bar. The 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 determines the working pressure 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
heather. See paragraph
3.6.3 Hot water side .
2.5.3 Temparature and Pressure valve (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
heater is under water supply pressure, cold water will automatically flow into it.
The valve remains open until the unsafe situation has been averted. A
connecting point for a T&P valve is standard on the water heater. See paragraph
3.6.3 Hot water side .
2.6 Indicators and
Alarms
2.6.1 Volt Free Contacts
Volt free contacts are supplied as standard to give remote indication/alarm of
'normal run' and 'lockout'. The 'lockout' indication includes shut down due to
operation of the safety thermostat, loss of flame and failure to ignite.