Fault And Alert Codes; Low Gas Pressure - A.O. Smith Cyclone XL 100 Series Service Handbook

Commercial gas water heaters

Table of Contents

1. LOW GAS PRESSURE

The minimum gas supply pressure is measured while gas is flowing (dynamic pressure) along with all additional gas appliances

operating on the same gas supply system. Cyclone XL water heater can operate smoothly when gas supply pressure is as low as 3.5"

WC dynamic for natural gas and 8.0" WC dynamic for LP models. There is no low gas pressure switch installed to the heater. If the gas

supply pressure is below the minimal as indicated on the heater rating plate, issues such as ignition failure, rough ignition and so on

may arise.

CHECK/ REPAIR:

• 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 SUPPLY SYSTEMS

Low pressure building gas supply systems are defined as those systems that cannot under any circumstances exceed 14" W.C. (1/2

PSI Gauge). These systems do not require additional pressure regulation. Measurements should be taken to insure that gas pressures

are stable and fall within the requirements stated on the water heater rating plate. Readings should be taken with all gas burning

equipment off (static pressure) and with all gas burning equipment running at maximum rate (dynamic pressure). The gas pressure

supplied to this unit must be below the maximum and above the minimum pressures listed on the unit's rating plate and must not drop

more than 1.5" W.C. when unit is operating at the high fire rate along with all additional gas appliances operating on the same gas

supply system. Pressure drops that exceed 1.5" W.C. may cause rough starting, noisy combustion or nuisance outages. Increases or

spikes in static pressure during off cycles may cause failure to ignite or in severe cases damage to appliance Gas Control Valves. If

your low pressure system does NOT meet these requirements, do not operate this unit. The installer is responsible for ensuring that the

gas supply pressures meet the requirements described above and listed in the table. Failure of the gas supply to meet these

requirements is not covered under the warranty.

High Pressure building supply systems use pressures that exceed 14" W.C. (1/2 PSI Gauge). These systems must use field supplied

regulators to lower the gas pressure to less than 14" W.C. (1/2 PSI Gauge). Water heaters require gas regulators that are properly sized

for the water heater's BTU input and capable of delivering the rating plate specified pressures. Gas supply systems where pressure

exceeds 5 PSI often require multiple regulators to achieve desired pressures. Systems in excess of 5 PSI building pressure should be

designed by gas delivery professionals for best performance. Water heaters connected to gas supply systems that exceed 14" W.C.

(1/2 PSI Gauge) must be equipped with a gas supply regulator capable of preventing the gas supplied to the unit from exceeding 14"

W.C. under any upstream supply pressure or condition.

SUPPLY GAS REGULATOR

The maximum allowable gas supply pressure for the water heaters covered in this Service Handbook is 14.0 inches W.C. (3.49 kPa)

static for natural and propane gas. Install a positive lock-up gas pressure regulator in the gas supply line if inlet gas pressure can

exceed these pressures at any time. Regulators must be sized to equal or exceed the BTU input requirements of the heater model and

installed, used, and maintained according to manufacturer's specifications.

If a positive lock-up regulator is installed follow these instructions:

1. Positive lock-up gas pressure regulators must be rated at or above the input Btu/hr rating of all the gas appliances that are on the same

system as the water heater.

2. Supply gas regulators shall have inlet and outlet connections not less than the minimum supply gas line size for the water heater they

supply.

3. Refer to the gas pressure regulator's manufacturers installation instructions to determine its installation location requirements.

4. After installing the positive lock-up gas pressure regulator(s) an initial nominal supply pressure setting of 7.0" W.C. (1.74 kPA) for

Natural Gas and 11.0" W.C. (2.74 kPA) for Propane (LP) while the water heater is operating is recommended and will generally provide

good water heater operation. Adjustments to the regulator maybe required to maintain a steady gas supply pressure.

5. When installing multiple water heaters in the same gas supply system it is recommended that individual positive lock-up gas pressure

regulators be installed at each unit from the supply gas connection on the water heater.