Start Up; Prior To Start Up; Initial Start Up - A.O. Smith BTH-120 Instruction Manual

prior to start up

Installation and start up of this water heater requires abilities
and skills equivalent to that of a licensed tradesman in the field
involved, see Qualifications on page 6.
Do not place the water heater in operation if any part has been
under water. Immediately call a qualified service technician to
inspect the water heater and to replace any part of the control
system and any gas control which has been under water.
Light the water heater in accordance with the Lighting and
Operation Instruction label on the water heater and in this manual
beginning on page 56.
The water heaters covered by this manual are equipped with an
electronic control system (see page 44) which automatically
sequences the Combustion Blower, pre and post purging of the
combustion chamber, the Hot Surface Igniter, the 24 Volt Gas
Valve, main Burner ignition, and flame sensing. The control
system will lock out after three unsuccessful ignition attempts.
Before attempting start up, thoroughly study and familiarize
yourself with the exact Sequence Of Operation, see the written
Sequence Of Operation on page 58 and the Sequence Of
Operation Flow Chart on page 59.
Be certain that the water heater is full of water, that air is purged
from the gas and water lines and that there are no leaks in the
gas and water lines. Ensure all inlet water valves are open.
filling the water heater
Follow these steps to fill the water heater prior to start up.
1. Close the heater drain valve.
2. Open a nearby hot water faucet to permit the air in the system
to escape.
3. Fully open the cold water inlet valve allowing the piping and
water heater to fill with water.
4. Close the hot water faucet opened in Step 2 as water starts
to flow.
supply gas line purging
Fire or Explosion Hazard
Gas line purging is required with new piping or systems in
which air has entered.
To avoid risk of fire or explosion purge discharge must not
enter into confined areas or spaces where ignition can occur.
The area must be well ventilated and all sources of ignition
must be deactivated or removed.
Use only the gas shown on the water heater rating label.
Keep ignition sources away from faucets after extended
periods of non-use.
Read instruction manual before
installing, using or servicing
water heater.
1. Close the main Gas Shutoff Valve, see Figure 52 on page 39.

start up

2. Purge all air from the supply gas line up to the water heater's
main Gas Shutoff Valve.
3. When all air has been purged from the supply gas line,
tighten all supply gas line connections.
4. Check for gas leaks, see Gas Line Leak Testing on page 40,
and repair any leaks found.

initial start up

reQuired test eQuipment
• Two U-tube manometers, recommended ranges; 0-14" W.C.
(0-3.5 kPa) and 0-35" W.C. (0-8.7 kPa) or pressure gauges.
• Two digital manometers can be used in place of U-tube
manometers or pressure gauges. recommended ranges;
-14.00 to +14.00" W.C. (0-3.5 kPa) resolution 0.01" W.C.
and 0-35" W.C. (0-8.7 kPa) resolution 0.10" W.C.
note: All test equipment must be acclimated to ambient
temperature before calibration and use.
preparation
1. Using the control system menus, change the Operating Set
Point to the lowest temperature setting, see Operating Set
Point And Differential Adjustment on page 47.
2. Turn the water heater's on/off switch to the "off" position.
3. Close the main Gas Shut Off Valve, see Figure 52 on page 39.
4. Wait five (5) minutes for any residual gas to clear.
5. Connect one manometer (higher range) to an available test
port for the supply gas pressure to the water heater:
On BTH 120 and 150 models there is a 1/8" NPT Tee fitting
and pipe nipple installed for the Low Gas Pressure switch
on the inlet side of the 24 Volt Gas Valve with a 1/8" pipe
plug for this purpose. remove the 1/8 inch pipe plug from the
bottom of the Tee fitting and install a barb fitting to connect
the manometer sensing tube, see Figure 58 on page 53.
On BTH 199 and 250 models there are test ports for supply
and manifold gas pressure readings on the gas valve. Using
a small flat tip pocket screw driver - open the needle valve
inside the supply gas pressure test port one full turn only;
turn the needle valve screw counter-clockwise to open the
valve. Slide the manometer sensing tube over the top of the
test port, see Figure 59 and Figure 60 on page 53.
6. Connect one manometer (lower range) to an available test
port for manifold gas pressure to the main Burner:
BTH 120 & 150 models: remove the 1/8 inch pipe plug from
the body of the gas valve on the outlet side and install a barb
fitting to connect the manometer sensing tube, see Figure 57
on page 53.
BTH 199 & 250 models: Using a small flat tip pocket
screw driver - open the needle valve inside the manifold
gas pressure test port one full turn only; turn the needle
valve screw counter-clockwise to open the valve. Slide the
manometer sensing tube over the top of the test port, see
Figure 59 and Figure 60 on page 53.
7. Open the main Gas Shutoff Valve.
8. measure and record the supply gas pressure, this is a "static"
supply gas pressure reading; while the water heater is not
firing. Adjust supply gas pressure as necessary, see Supply
Gas Pressure Adjustment on page 54.
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