________________________________________________________________________________
47
AST 14 C 255/00
During DHW modulation, once the min. gas flow rate is reached and with the supplied
output above the required one, the burner is switched off when DHW temperature reaches
the + 5°C set-point value. After burner switching off, whilst the operation request is still
present, burner will be ignited again when the temperature falls below the + 3°C set-point.
During the first 20 seconds when the DHW is being drawn, to avoid boiler continuous
"switch on/off", the maximum temperature allowed by the DHW probe to switch off the
burner is set to 15°C higher than the set-point, whereas to switch it on again the
temperature must fall below the + 8°C set-point.
During the plate DHW modulation mode, the boiler pump is supplied with power and the
deviating valve is in DHW position, whereas the multifunction relay is in the rest condition.
Warning: the burner is switched off also in case the flow probe detects a value of 85°C
and then ignited again (with the request still present) only upon reaching 80°C.
Plate DHW modulation temperatures:
DHW temperature setting range: 35 °C ÷ 57 °C
DHW thermostat triggering temperature OFF = set point + 5°C
DHW thermostat triggering temperature ON = set point + 3°C
DHW thermostat triggering temp. initial draw (first 20 sec) OFF = set point + 15° C
DHW thermostat triggering temp. initial draw (first 20 sec) ON = set point + 8° C
Flow water thermostat triggering temperature with plate DHW mode: OFF 85° C
Flow water thermostat triggering temperature with plate DHW mode: ON 80° C
Flow water PID triggering temperature with DHW mode: 81° C
Flow water PID deactivating temperature with DHW mode: 75° C
N.B. In case the boiler is combined with a solar plant with instantaneous-type integration, it is
recommended setting parameter P14 to 1. This increases the modulation range, avoiding boiler
hunting (start and stop) with inlet temperature very close to the set-point. In such case, the limit
temperatures are as follows:
DHW thermostat triggering temp. OFF with instantaneous solar integr.: set-point + 10° C
DHW thermostat triggering temp. ON with instantaneous solar integr.: set-point + 9° C
BOILER
DHW MODULATION
(only for RTFS version with water heater, P3=3)
With boiler running in “DHW” or “DHW + CH” mode, the boiler programme enable time
generates a request in DHW mode.
If the water heater temperature read by the NTC probe is lower than the boiler priority
thermostat ON triggering temperature (set-point - 3°C) set either through boiler or through
remote control and the flow temperature is lower than 70°C, the burner ignition sequence
is started with the automatic flame control section enabling.
At the end of this sequence, the power supplied to the burner corresponds to the flame
modulation value which, thanks to a PID-type action, allows to reach and maintain the flow
modulation temperature in boiler mode. Such temperature is calculated according to the
requested boiler temperature and of the current temperature read by the probe, and shall
in any way lie within a lower value (corresponding to "requested boiler temperature +
10°C”) and a higher value (85°C). Max. flow modulation occurs when the difference
between requested boiler temperature and current boiler temperature is higher or equal to
10°C.
