Top Views - A.O. Smith BTH-120 Instruction Manual

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Bth 120 & 150 components
1. Water Heater's 120 VAC on/off switch.
2. Powered anode rods. The water heater's covered in this
manual are equipped with powered (non sacrificial) anode
rod(s). The BTH 120 has one powered anode, all other models
will have two. Protective current is fed by the control system
to the titanium electrodes at the end of each anode rod. This
current flows through the water to the conductive surfaces
inside the storage tank which diminishes the corrosive effect
(rusting) of water when it comes in contact with steel.
3. Central Control Board (CCB) enclosure. This enclosure
houses the control system's main circuit board. The CCB
regulates water temperature and controls all water heater
functions, see Control System Operation on page 44.
4. Intake air connection - 3 inch PVC.
5. 120 VAC junction box. Incoming power supply and ground
connections are made here. See Power Supply on page 14.
6. Water heater's 24 Volt Gas Valve.
7. Supply gas line connection. See the requirements for the
Gas Supply Systems on page 14.
8. Low Gas Pressure switch. Normally open contacts that
close on a rise in pressure. This switch is used to insure
supply gas pressure is above minimum requirements. The
control system monitors this switch and will disable heating
operation if its contacts are open during a heating cycle. See
Gas Pressure requirements and Table 3 on page 12.
9. Blocked Intake Air switch. Normally closed contacts that
open on fall in pressure. This switch is used to insure intake
(combustion) air to the water heater is not restricted. The
control system monitors this switch and will disable heating
operation if its contacts are open during a heating cycle.
120,000 & 150,000
Btu/hr MODELS
TOP VIEW
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10. Vent connection (exhaust elbow) - 3 inch PVC.
11. Combustion Blower.
12. Blocked Exhaust (vent) switch. Normally closed contacts that
open on a rise in pressure. This switch is used to insure the
Exhaust (vent) piping connected to the water heater is not
restricted. The control system monitors this switch and will
disable heating operation if its contacts are open during a
heating cycle.
13. Blower Prover switch. Normally open contacts that close on a
rise in pressure. This switch is used to insure the Combustion
Blower is operating properly. The control system monitors
this switch and will disable heating operation if its contacts
are closed before the Combustion Blower is energized or
open any time during a heating cycle. See Sequence Of
Operation on page 58.
14. Temperature-Pressure relief Valve. See Temperature-
Pressure relief Valve on page 16.
15. Upper Temperature Probe, 1 of 2 temperature probes. The
water heater's control system monitors this probe to detect
water temperature in the upper portion of the storage tank.
The Upper Temperature Probe also houses the ECO (energy
cut out) switch. This is a non adjustable high temperature
limit switch. The ECO switch contacts are normally closed
and will open on a temperature rise. See High Temperature
Limit Control (ECO) on page 43.
16. Water outlet connection 1 1/2" NPT.
17. UIm (user interface module). The UIm includes the display
circuit board, the control system's LCD display and
operational buttons. Used to adjust various user settings and
view operational information. See Control System Operation
on page 44.
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