A.O. Smith VB/VW 500/750/1000 Manuale Utente

•  Measure the incoming gas pressure. -Minimum inlet gas supply pressure of 4” w.c. and maximum is 11.0 for natural gas or

8” w.c. min and 13.8 max for propane. The maximum value specified must not be exceeded under both load and no load

conditions. If this condition can not be obtained a positive lock-up type pressure regulator MUST be installed approximately

five feet away from the gas valve of the boiler and per the regulator manufacture’s instructions.

•  Check all gas supply lines for leaks.
•  Check that all venting is properly installed in accordance with the venting section of the instruction manual.
Follow the lighting and operating instructions in the Instruction Manual.  

  - The boiler is tested at the factory and should start properly if installed in accordance with the boiler’s instruction manual.

  - Before starting the boiler, refer to the temperature set-point procedure section in the boilers instruction manual.

 - Turn on the boiler’s on/off switch. Ensure the operating set point is set high enough to activate a call for heat. If an external

control is using the boiler’s Enable/Disable circuit, ensure that the external control’s contacts are closed. If there is no

external control, ensure that the two wires provided for this circuit are wire-nutted together in the junction box on the back

of the boiler. Refer to the wiring diagram on the boiler.

  - Allow the unit to run for at least 10 minutes before proceeding with the combustion analysis. Take a combustion sample and 

record CO and CO

2

 or O

2 

readings.

  - On UIM go to main menu, scroll down to user settings and press select. Scroll down to MOD mode, press select. Use

the up and down keys to select options: MIN (MINIMUM FIRING RATE). MAX (MAXIMUM FIRING RATE). MOD (FOR

AUTOMATIC MODULATION MODE). Press select for the desired option. For checking the combustion setup on MIN or

MAX the boiler will remain in this state for 20 minutes before defaulting to the MOD (modulation) mode.

 - First set boiler to the “Test Mode Max,” as described above, to achieve maximum firing rate of the boiler. Check combustion

readings using a combustion analyzer. If combustion readings are not in accordance with the chart below adjust as follows: remove

the flat, round, blue plastic cap from the cover. Using a 3mm (7/64”) hex wrench, turn the adjustment screw counterclockwise to

increase or clockwise to decrease gas flow and achieve the desired CO

2

  level. See Table referenced below for correct settings. 

There will be a slight time delay between the adjustment and the response of the CO

2

measuring instrument. Adjust the settings

in small 1/16 increments and allow the combustion readings to stabilize before readjusting. When desired adjustments are

complete, reinstall the blue plastic cap on the cover. Combustion samples shall be taken within 8 inches from the rear boiler. 

IMPROPER ADJUSTMENT CAN CAUSE INCOMPLETE COMBUSTION RESULTING IN DEATH.

 - Next set boiler to the “Test Mode Min,” as described above, to achieve minimum firing rate of the boiler. Check combustion

readings using a combustion analyzer. If combustion readings are not in accordance with the chart shown below adjust as

follows: remove the metal cap on the gas regulator using a slotted screwdriver. This will expose the offset adjustment screw.

Using a TORX® T40 or a 5mm hex wrench, carefully adjust the low fire gas setting to achieve the CO

2

 level prescribed 

in below reference table. Note: The rotation of the Low Fire adjustment is opposite of the High Fire as follows: Clockwise

rotation increases gas flow, counterclockwise rotation decreases gas flow. Adjustments to the offset pressure regulators

should not exceed 1/16 increments at a time before allowing the readings to respond and stabilize. After proper low fire

offset adjustment is made, reinstall the slotted cap on the regulator.

Following all gas valve adjustments, check for proper light-off and verify correct fuel/air mix during test mode procedure prescribed above.

If adjustments have been made, repeat the combustion sampling using the “Test Mode” procedure to insure that the readings remain

within the ranges. If the readings are not in accordance repeat the High and Low fire adjustment procedure.

 

IMPORTANT!! The Min Mode and Max Mode are used for checking combustion during start up. Return boiler to Mod Mode after

checking combustion.  

% CO

2

, for Natural Gas @ 

max input

8.0% - 9.5%

% CO

2

, for Propane Gas @ 

max input

8.5% - 10.0%

CO PPM

< 200 PPM

% CO

2

, for Natural Gas @ 

min input

6.5% - 7.5%

% CO

2

, for Propane Gas @ 

min input

7.5% - 8.5%

CO PPM

< 100 PPM