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SECTION C: Installation
31
To make an adjustment to a setting in the control, begin
by selecting the “ADJUST” menu. To change from the
view menu to the adjust menu, simultaneously press
and hold all three buttons for 1 second. The menu
name, “ADJUST” will be displayed in the menu field.
The menu will automatically revert back to the view
menu after 20 seconds of keyboard inactivity. Then
scroll to the desired item using the scroll button. Fi-
nally, use the ▲or ▼ button to make the adjustment.
In the absence of other information, the values pro-
vided in Table N should be used as default settings.
Heater Sequence of Operation
Model 503 - 1503
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 pump
relay, the N.O. contacts of blower relay, the
120/24 VAC transformer, and terminals L1 and F1
of the ignition module are powered.
3. The 120/24 VAC transformer sends a 24 VAC hot
power signal to the 24V Terminal Block .
4. 24 VAC is sent from the 24V Terminal Block to
the NO pump contacts on the modulating tempera-
ture control (pin #13), to pin TP2 of the optional
alarm relay, to terminal R of the alarm circuit on
the modulating temperature control (pin #24) and
the green “Power On” LED on the front of the
heater will illuminate.
5. 24 VAC power is sent from 24V Terminal Block
to Pin P1-1 of the UDB board, the 24 VAC termi-
nal of the ignition control module, the NC contact
of the manual high limit, and L1 of the Low Water
Cut Off (if equipped).
24 VAC is sent from the NC contacts of the man-
ual high limit to pin P3-1 & P3-2 of the UDB
board.
Upon loss of water in the heater, the Low Water
Cut Off (if equipped) will send a 24 VAC signal to
pin P3-4 of the UDB board to indicate a safety
fault.
6. A 24 VAC signal is sent from the NO contacts of
the Low Water Cut Off to the common terminal of
the Blocked Vent Switch.
During a blocked vent condition a 24 VAC signal
is sent from the NO open contacts of the Blocked
Vent Switch to pin P3-5 of the UDB board to indi-
cate a safety fault.
7. During normal operation of the heater the 24 VAC
signal exits the NC contacts of the Blocked Vent
Switch and is sent to the common terminal, of the
Low Gas Pressure Switch (if equipped).
During a low gas pressure condition 24 VAC is
sent from the NC contacts of the Low Gas Pres-
sure Switch to pin P3-6 of the UDB board to
indicate a safety fault.
8. 24 VAC is sent from the NO contacts of the Low
Gas Pressure Switch to the common terminal of
the High Gas Pressure Switch (if equipped).
During a high gas pressure condition 24 VAC is
sent from the NO contacts of the High Gas Pres-
sure Switch to pin P3-7 of the UDB board to
indicate a safety fault.
9. 24 VAC is sent from the NC contacts of the High
Gas Pressure Switch to the common terminal of
the Auto Reset High Limit (if equipped) and to en-
ergize the coil of optional alarm relay.
If the Auto Hi Limit opens, 24 VAC is sent from
the NO contacts of the Auto Hi Limit to pin P3-3
of the UDB board to indicate a safety fault.
10. 24 VAC is sent from the NC contacts of the Auto
Reset Hi Limit to the common terminal of time de-
lay relay.
11. 24 VAC is sent from the NC contacts of time delay
relay to the common terminal of the burner switch
located on the front exterior panel of the heater.
12. Power then travels to the enable/disable connec-
tion and to the Ht D (heat demand) connection of
the modulating temperature control.
Power splits from the enable/disable and goes to
the stage contact of the modulating temperature
control (pin #15).
13. When the stage contact closes on the modulating
temperature control, 24 VAC is sent to the com-
mon terminal of the flow switch and to pin P1-3