12
HEATING BOILERS: Astra G-120E
the socket on the rear control panel indicated with
symbol .
• REMOVING THE ROOFTOP COVER OF
THE BOILER
Before detaching the rooftop panel of the boiler,
unplug it from the electrical supply. Take off the
loose cover 22 (Fig. 1). The rooftop panel is removed
in the following sequence (Fig. 7): 1) unscrew two
fastening bolts, 2) lift the backside part of the
cover, 3) push the cover forward, 4) lift it.
• CONTROLLING THE TEMPERATURE OF
WATER RETURNING TO THE BOILER
It is absolutely necessary to maintain the
temperature of the water returning from the
heating system to the boiler at a constant level, no less than 65°C, as this will prolong the lifetime of the boiler and will make
the combustion process more effective. This is because when a constant high temperature of water returning to the boiler
is maintained, there arises significantly less water vapour condensation inside the boiler. The heavy water condensation is
harmful to the boiler, because deposits of tar, pitch and soot accumulate on the walls of the heat exchanger, causing intense
metal corrosion. Moreover, the resulting layer of soot impedes effective heat transfer and the efficiency of the boiler falls.
In order to maintain the temperature, we recommend installing the small circulation circle together with a Swedish-made
thermoregulation device, “Laddomat 21-100”. Make sure that the “Laddomat” is supplied with the 72°C thermostat cartridge.
The mentioned temperature is the one at which the valve of the device opens completely. However, the actual temperature
of the water returning from the system and getting into the boiler after mixing, is 5-6°C lower. The higher the temperature
of the return water is, the better it is for the boiler. Thermoregulation devices of other manufacturers could be used for
maintaining the temperature of the returning water as well.
• HEATING OUTPUT, WATER TEMPERATURE AND WATER FLOW RELATIONSHIP
The heating output supplied to a heating system depends directly
upon the difference of flow and return water temperatures Δt and
the intensity of the water flow circulating through the boiler. The
boiler will fail to reach the desired temperature of the flow water
if the returning water temperature is too cold or the circulation
pump is too powerful. This will happen because the boiler will be
forced to produce a larger heating output than it has been designed
for. The most effective boiler operation occurs when the difference
between the flow and return water temperatures is 13-18°C. If the
boiler is forced to operate with a 20°C or even greater temperature
difference, it will work ineffectively, consume too much of fuel, and
the combustion period of one fuel load will consequently shorten.
If the previously mentioned difference of temperatures is kept less
than 10°C, the fuel in the boiler will again burn inefficiently and fume
because of a lack of air supply. If you know the water flow intensity
near your boiler, in the above presented table you can check, what the
difference of flow and return temperatures your boiler is capable to
maintain, when operating at the nominal heating output.
Fig. 7 Removing the rooftop cover of the boiler
1. Unscrew bolts; 2. Lift the backside of the cover; 3. Push the cover forward; 4. Raise
the cover.
1
1
2
3
4
Difference of water temperatures
Δt, °C
Heating output, kW
120
Water flow, l/min
11
147
12
134
13
124
14
115
15
107
16
101
17
95
18
90
19
85
20
81
21
77
22
73
23
70
24
67
25
64
