________________________________________________________________________________
46
AST 14 C 255/00
DHW CONTROL
With boiler running in “DHW” or “DHW + CH” mode, a flow rate exceeding 2.5 litres/minute
within the flowmeter (CTFS version) or boiler programme enabling (RTFS version with
water heater), generates a DHW operation request, thus starting "DHW modulation".
The operation request in DHW mode has the priority over all other requests, and finishes
when the previously mentioned electric contacts are opened again.
WARNING: only for combined instantaneous versions (CTFS), with parameter P15, it
is possible to delay the flowmeter reading for the DHW mode (from 0 to 10 seconds).
PLATE DHW MODULATION
(only for combined version, P3=1)
Upon an operation request in plate DHW mode, if the water temperature read by the
domestic hot water NTC probe is lower than the set-point value + 3°C (plate DHW
thermostat triggering temperature ON), the burner ignition sequence is started with the
automatic flame control enabling.
Immediately after burner ignition, gas flow rate corresponds to flame modulation value
which, thanks to a PID-type action, allows to reach and maintain the set DHW
temperature.
In case of poor heat output by the plate exchanger due to possible clogging and
consequent overtemperature of the primary body, another PID-type setting on the flow line
is added to the DHW modulation. Such operation occurs at a flow temperature higher than
81°C and disables when the flow temperature falls below 75°C. In presence of double
modulation, the gas flow rate supplied to the burner corresponds to the lowest modulation
value.
Modulation with P6=0
80% Pmax
