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SECTION C: Installation
32
(CFH) of the UDB board. In addition, the amber
“Call-for-Heat” LED on the front of the heater will
illuminate.
14. The pump contact on the modulating temperature
control closes sending 24 VAC to the pump switch
located on the front exterior panel of the heater.
15. When the pump switch is closed, 24 VAC is sent
to the coil of the pump relay.
16. The pump relay energizes and closes the contacts,
starting the heater pump.
17. Upon sufficient flow, the flow switch closes and
sends 24 VAC to the common terminal of the air
pressure switch, TH terminal of the ignition mod-
ule, coil of the ignition lockout relay and the NO
contacts of the ignition lockout relay.
If the flow switch does not close, a 24 VAC signal
is sent to pin P4-9 of the UDB board to indicate an
insufficient flow condition.
When the 24 VAC signal is sent to P4-9 the same
signal then de-energizes the coil of time delay re-
lay to remove a heat demand from the modulating
temperature control and restart the ignition se-
quence after the 5 second time delay.
Upon ignition lockout, the module energizes the
ignition lockout relay and sends a 24 VAC signal
to pin P4-12 (ignition lockout) of the UDB board.
18. When 24 VAC is received at TH on the ignition
module, the contacts between pins F1 and F2 close
and send 120 VAC to pin 1 of the blower relay.
19. The coil of the blower relay energizes closing the
NO contacts sending 120 VAC to energize the
combustion air blower motor.
The combustion air blower will operate at 50% of
capacity for approximately ninety (90) seconds be-
fore the modulating signal from the modulating
temperature control will control the fan speed in
relationship to the system water temperature.
20. Once sufficient air pressure is achieved in the
heater and the air pressure switch closes the NO
contacts, 24 VAC is sent to the heater interlock
connection on the ignition module.
If air pressure is insufficient or lost during heater
operation a 24 VAC signal is sent from the NC
contacts of the air pressure switch to pin P4-10 of
the UDB board to indicate insufficient air pressure.
When the 24 VAC signal is sent to P4-10 the same
signal then de-energizes the coil of the time delay
relay to remove a heat demand from the modulat-
ing temperature control and restart the ignition
sequence after the 5 second time delay.
21. After receiving 24 VAC at the heater interlock,
power then travels to the P Switch terminal of the
ignition module.
The ignition module employs a 15 second pre-
purge before the next sequence.
22. After 15 seconds of combustion chamber pre-
purge, pin S1 sends 120 VAC to the Hot Surface
Igniter.
23. The Hot Surface Igniter will be energized for ap-
proximately 30 seconds and must exceed 3.1 amp
draw during heat up.
24. Once the ignition module determines the proper
operation of the Hot Surface Igniter, a 24 VAC
signal is output from the Valve pin on the module
to energize the gas valve.
25. The gas valve is energized and the blue “Burner
On” LED on the front of the heater energizes.
26. The remote sensor is now trying to rectify the
flame. If the flame is not rectified within 4 seconds,
the ignition module will shut down the gas valve
and lock out.
27. When burner flame is rectified, the gas valve will
remain at 50% fire for the remainder of the ninety
(90) second delay after the CFH was initiated and
then modulate in relationship to the output signal
to the combustion air blower from the modulating
temperature control.
28. When the CFH is satisfied, the heater will return to
a standby condition awaiting the next CFH.
Model 1753 – 2003
1. The black (hot) wire lead, located at the right-
middle front inside the control compartment, goes
directly to the main power switch.
2. When the main power switch is placed in the
“ON” position, the 120 VAC terminal block in the
control compartment, the N.O. contacts of the