Main Burner; Pre-Troubleshooting; Troubleshooting - A.O. Smith DB/DW-720-1810 User Manual

1. Remove main burners from unit.
2. Check that burner venturi and ports are free of foreign matter.
3. Clean burners with bristle brush and/or vacuum cleaner 3/4"
DO NOT distort burner ports or pilot location.
4. Reinstall burners in unit. Making sure front and rear of burners
are installed correctly in burner support brackets.
Also check for good flow of combustion and ventilating air to the
unit. Maintain a clear area around the boiler at all times.
After placing the boiler in operation check the ignition system safety
shutoff devices for proper operation. To accomplish this with the
main burners operating, close the pilot adjusting valve on the left
side of the manifold. Within four seconds the main burners and
pilot should extinguish and the spark igniter on the pilot assembly
should begin sparking. If this does not occur immediately,
discontinue gas supply by closing main manual shutoff and call a
qualified serviceman to correct the situation. If the burners
extinguish, and pilot assembly begins sparking, the system is
operating correctly so discontinue electrical power, open pilot
adjusting valve, and light boiler in accordance with lighting and
operating instructions.
For installations above 2000 feet (600 m), refer to HIGH ALTITUDE
INSTALLATIONS in the installation section.
CHECKOUT SEQUENCE
Set tank/system temperature
control (thermostat) 20°F (12°C)
below tank water temperature.
Set tank/system temperature
control (thermostat) 20°F
(12°C) above tank/system
water temperature.
Boiler outlet temperature
exceeds 210°F (98°C) hot water
supply, 250°F (120°C) hydronic
supply.
Set tank/system temperature
control (thermostat) for desired
water temperature.
TROUBLE-SHOOTING
SYSTEM OPERATION
CORRECT INCORRECT
Circulating pump Pump and burner
and burner remain on.
shutoff.
With thermal Circulating pump
balancer, pump on.
off delay of Burner on.
approximately
two minutes.
Circulating pump Circulating pump
and burner on. on.
Circulating pump
and burner off.
Burner on.
Circulating pump. Circulating pump
and burner on.
System maintains
desired water
temperature.
35
PRE-TROUBLE-SHOOTING
Before any extensive trouble-shooting, perform the following:
Ensure that:
— Power (120 vac) is supplied to the appliance.
— System control (tank temperature control, thermostat, etc.) is
calling for appliance operation (call for heat).
— Other contacts (switches) are closed (transformer relay, low
water cutoff, flow switch, limit controls, pressure switches, etc.)
— Gas supply pressure is within the maximum and minimum
operating ranges listed on the appliance rating plate/label.
— Voltage (24 vac) is supplied by transformer.
— Appliance is wired according to wiring diagram.
NOTE: Cross wiring the 24 volt circuit of the relay will short the
transformer.
— All wire terminals/connectors are firmly attached to valves,
modules, switches, limit controls, etc.
— There has been no damage caused by freezing, inoperative
pumps, etc.
CAUSE
Temp. control
(thermostat) defective.
System wiring
incorrect
Pump wired for
continuous operation.
Gas valve stuck
or defective.
System wiring is
incorrect.
Auto reset high limit
control set too low.
Auto reset high limit control
differential too wide.
System wiring is
incorrect.
Manual reset high limit
switch has activated.
Gas valve or wiring
defective.
Power off or system
wiring is incorrect.
Temp. control
(thermostat) defective.
System wiring is
incorrect.
Auto reset high limit control
defective, or set too
high (max. should
be set at 200°F [93°C] hot
water supply, 240°F
[115°C] hydronic supply).
REMEDY
Replace.
Correct wiring.
Correct wiring.
Correct or replace
valve.
Correct wiring.
Replace. (If problem
proven to be at this
control by applying
jumper to terminals).
Correct wiring.
Depress reset
button.
Check power supply
and wiring.
Replace.
Correct wiring.
Replace.