Reznor RDH Series User Manual

1307SDH_RDH--EN,page 19/32
Figure 12 : Ignition system
The SDH/RDH heater is equipped with a direct spark integrated control relay. The control relay monitors the safety
devices and controls the operation of the venter motor and the gas valve between heat cycles.
The time line below illustrates a normal heat cycle.
The time line below illustrates a normal heat cycle.
Definitions
•Start position: The system is not in lockout position and can proceed with the start-up sequence upon a demand for
heat.
•Pre-purge time: This is a period of 20 seconds during which the combustion fan (venter) operates prior to activation
of the ignition device.
•Safety time: The safety time is the delay between the gas valve being energized and the flame sensor checking
for the presence of a flame. This is a period of 5 seconds.
Note
: If no flame is sensed, the burner relay will attempt ignition 5 times before going into lock-
out mode.
•Post-purge time: This is the time of 10 seconds between burner shutdown and the moment the combustion fan (venter)
is de-energized.
Start pre-purge
Energisation of venter motor.
If the differential pressure switch
is in normally closed position
(start position).
Power to gas valve and ignitor
Sensor checks for the presence of a flame
End of heat demand.
De-energisation of gas valve.
De-energisation of venter motor
First heat demand signal.
Check on pressure switch.
Must be in closed or start position.
If not, there will be no power to
the venter motor.
The power to the burner relay is off
until the pressure switch goes to
normally closed - or start position.
Safety check on flame sensor.
If there is a flame, the relay will
go to lock-out. The light in the red reset
switch, mounted visibly on the heater
will glow.
Line output during ignition time to control
high fire start on two stage or modulation
applications.
If no flame, then repeat starting
at pre-purge for 5 attempts.
If no ionisation after 5 attempts, then
lock-out.
Pre-purge
time
Ignition
time=
Safety
time
Normal operation
of burner relay
Post-purge time
20 sec 5 sec 10 sec
time
Start position

Reznor RDH Series Specifications

General

Brand	Reznor
Model	RDH Series
Category	Air Handlers
Language	English