Fault And Warning Codes; Low Gas Pressure; High Altitude; Gas Pressure Specifications - A.O. Smith BTH 120 Service Handbook

FAULT AND WARNING CODES

1. LOW GAS PRESSURE

Low Gas Pressure
Fault occurred 2 mins ago
Gas pressure is below minimum
required to operate this unit. Check
gas pressure and switch.
Call a service professional:
Your Company Name Here
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CHANGE
CHECK/ REPAIR:
• Check Low Gas Pressure Switch wiring and connectors. Connectors must be clean and tight.
• Determine proper minimum pressure from rating plate.
• Use manometer or gauge to check gas pressure during all stages of operation with all other
appliances firing.
• If pressure falls below rating plate requirement, supply pipe may be too small for application or supply
regulator may be operating improperly. See Gas Pressure section below.

HIGH ALTITUDE

The water heaters covered in this Service Handbook are certified for elevations up to 10,100 feet (3,078
meters). For higher elevations call the toll free support phone number shown on the back cover of this
Service Handbook for technical assistance.

GAS PRESSURE SPECIFICATIONS

MODELS
Maximum Gas Supply
Pressure
Nominal Gas Supply
Pressure
Minimum Gas Supply
Pressure (Low Gas
Press. Switch Setting)
*Manifold Pressure
*The Manifold Pressure is the factory setting and is not adjustable. A negative pressure will be seen with just the blower running without
the Gas Control Valve open.
ADVANCED
BACK
Natural
120-250
14.0" WC
(3.49 kPa)
7.0" WC
(1.74 kPa)
4.4" WC
(1.10 kPa)
0" WC
(0 kPa)
Servicing should only be performed by a Qualified Service Technician
CAUSES:
• The Low Gas Pressure Switch is detecting gas
pressure below the value required for proper
operation.
Propane Natural
120-250 300/400/500
14.0" WC 14.0" WC
(3.49 kPa) (3.49 kPa)
11.0" WC 7.0" WC
(2.74 kPa) (1.74 kPa)
8.5" WC 4.8" WC
(2.12 kPa) (1.19 kPa)
0" WC
(0 kPa) (0 kPa)
Propane
300/400/500
14.0" WC
(3.49 kPa)
11.0" WC
(2.74 kPa)
8.5" WC
(2.12 kPa)
0" WC 0" WC
(0 kPa)
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