The control unit monitories the primary air flow to the burner by varying the fan motor
power supply voltage (DC), ensuring a correct variable speed during the operation
according to the output needed in MPP range while in LPP the fan have a fixed speed due
to the unit be fix power version.
The fan motor provides an additional control signal to enable/disable operation and the
speed of the fan is measured by the feedback signal provided by the fan's motor. The
signal consists on a square wave with a frequency proportional to the speed of the fan.
In order to simplify the after sales stock of parts, the modes share same type of fan according:
Low Power Fan:
MPP1 12/15 shares same fan of MPP2 12
High Power Fan:
MPP1 17 shares same fan of MPP2 15/17
4.5 Gas Valve
Over the control unit it is possible to control the gas flow to the burner by the modulating
gas valve (MV1). This valve controls the thermal load in order to ensure the correct hot
water set temperature, under water flow or temperature variations.
The gas valve is composed by other solenoids identified as safety valves (SV + SV1 +
SV2) releasing the modulated gas to and from the solenoid gas valve.
The safety valve (SV) is the first main safety element that releases gas to the burner and
the safety valves 1 (SV1) and 2 (SV2) are the second safety level elements, that release
gas to the first and second burner segments, respectively, acting as safety and
The burner is composed by 2 segments which are fed according to the solenoid valves
activation (SV2 and/or SV3) which can be switched over according to the different thermal
load, in order to obtain a stable combustion. These valves ensure the most suitable
condition under the control of microcomputer, based on the values detected by the water
flow sensor and hot water thermal sensors.
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Pict. 15 – DC Fan (WTD-3&4 / T5600&T5700)
6 720 887 547 "SM FP_ErP MPP Europe 2018/08 en"