2
Mynute 24m
SECTION 1
DESIGN PRINCIPLES AND OPERATING SEQUENCE
Fig. 2
1.1
PRINCIPLE COMPONENTS
•
A fully integrated electronic control board featur-
ing electronic temperature control, anti-cycle
control, pump over-run, self-diagnostic fault in-
dicator, continuous gas modulation
•
Low-water content copper heat exchanger
•
Electronic ignition with flame supervision
•
Integral pump
•
Fan
•
Expension vessel
•
Differential air pressure switch
•
Water pressure switch
•
Two-stage gas valve
•
Pressure gauge
•••••
Safety valve.
1.2
MODE OF OPERATION
When there is a request for heat and or hot water
via the programmer/time clock and/or any external
control, the pump and fan are started, the fan
proves the differential air pressure switch which
inturn allows an ignition sequence to begin. Igni-
tion is sensed by the electronic circuitry to ensure
flame stability at the burner. Once successful
ignition has been achieved, the electronic circuitry
increases the gas rate to 75% for a period of 15
minutes. Thereafter, the boiler’s output will either
be increase to maximum or modulate to suit the
set requirement.
When the appliance reaches the desired tempera-
ture the burner will shut down and the boiler will
perform a three-minute anti cycle (timer delay).
When the request for heat and/or hot water has
been satisfied the appliance pump and fan may
continue to operate to dissipate any residual heat
within the appliance.
1.3
SAFETY DEVICES
When the appliance is in use, safe operation is
ensured by.
•
a water pressure switch that monitors system
water pressure and will de-activate the pump,
fan, and burner should the system water pres-
sure drop below the rated tolerance;
•
a high limit thermostat that over-rides the tem-
perature control circuit to prevent or interrupt the
operation of the burner;
•
a differential air pressure switch that checks the
operation of the fan and flue thereby allowing
safe operation of the burner;
•
a safety valve which releases excess pressure
from the primary circuit.
CH
return
CH
flow
primary
NTC sensor
safety
valve
circulator
expansion
vessel
main heat
exchanger
burner
gas valve
water
pressure switch
automatic
by-pass
discharge
valve