Hydronic Heating Boilers and Domestic Water Heaters Installation and Service Manual

CLEANING AND
MAINTENANCE
CONTINUED
A faulty hot surface igniter or ignition module must be
replaced with an identical part. A specification igniter and
ignition module for this specific unit is available from your
local distributor. Do not use general purpose field
replacement ignition modules or igniters.
Ignition System Checkout
1. Turn off gas supply to unit.
2. Turn electric power on.
3. Adjust the set point on the temperature control to a setting
above water temperature or to the highest safe setting.
4. The igniter will cycle on trial for ignition.
5. The ignition module will lock out and turn the alarm light on.
6. Adjust the Set Point Differential and High-Fire Offset to the
desired settings.
7. Turn on gas supply.
8. Press the module reset button to reset the ignition module.
This is a red button beside the ignition module or on the
diagnostic panel on the header-end of the unit.
9. If ignition system fails to operate properly, repair work must
be performed by a qualified service person or installer.
SEQUENCE OF OPERATION
OVERVIEW
This sequence of operation can be considered the order of
events in sequential order that occur after the appliance has
received a call for heat. The process begins with 120VAC
power entering the appliance and ends with the appliance
going into an idle state after completion of a successful call for
heat.
Note: The following descriptions do not include remotely
connected devices that may be connected to the appliance.
Refer to the wiring diagram for actual point to point wiring
connections that show power delivery.
1. The POWER switch is placed in the “ON” position.
2. 120VAC power is supplied to the control transformer
along with L1 and F1 on the ignition module.
3. 24VAC is supplied to the electronic temperature control,
the ignition module and the adjustable high limit control.
4. 24VAC is then supplied to the auxiliary limit control (if
equipped).
5. If equipped, 24VAC is supplied to a low water cut-off and
then to the high and low gas pressure switches.
6. 24VAC is supplied to the continuous alarm terminals A1
and A2 and then to the remote stage one terminal strip, 1C
and 1NO.
7. 24VAC is supplied to the electronic temperature control.
8. The electronic temperature control then calls for heat.
9. 24VAC is supplied to the intermittent alarm field safety
contacts, B1 and B2.
10. 24VAC is supplied to the water flow switch (if equipped).
11. 24VAC is supplied to the TH terminals on the ignition
module.
12. As power is applied to the TH terminals on the ignition
module, 120VAC is switched from the F2 terminal to start
the combustion air fan at full speed on the 495,000 -
745,000 Btu/hr models and at low speed on the 985,000 -
2,065,000 Btu/hr models.
13. 24VAC is supplied to the C terminal of the air pressure
switch. As the low air switch makes, power is supplied to
the ignition module.
14. 24VAC is then supplied to the PS terminals on the ignition
module as the air pressure switch makes to prove fan
operation..
15. The combustion air fan operates for the pre-purge period.
16. At the end of the pre-purge, 120VAC is applied to the hot
surface igniter and the trial for ignition light.
17. The hot surface igniter proves 1800 F (982 C) ignition
temperature by current draw through the ignition module.
18. The ignition module supplies voltage to the MV terminals
on to the gas valve(s).
F9 SINGLE STAGE FIRING
19. All gas valves on the 495,000 - 745,000 Btu/hr models and
approximately half of the valves on the 985,000 -
2,065,000 Btu/hr models open, supplying gas to the orifice
and burner inlet to pre-mix.
20. The gas/air mixture is forced into the burner and out of the
burner ports under pressure.
21. The hot surface igniter lights the gas/air mixture and then
serves as a flame sensor to prove main burner flame by
rectification.
22. After a time delay of 10 seconds, the remaining gas valves
on the 985,000 - 2,065,000 Btu/hr models open, supplying
gas to the remaining burners.
23. The gas/air mixture is forced out of the burners and out of
the burner ports under pressure.
24. The burners light by carryover from the burners currently
firing.
25. The heater is now firing at full rated input.
M9 MODULE FIRING
26. The first stage gas valve(s) opens and supplies gas to the
orifice and burner inlet to pre-mix.
27. The gas/air mixture is forced into the burner and out of the
burner ports under pressure.
28. The hot surface igniter lights the gas/air mixture and then
serves as a flame sensor to prove main burner flame by
rectification.
Hydronic Heating Boilers and
Domestic Water Heaters
44