A.O. Smith BTH 300A, BTH 400A Noisy Burner Operation, GAS Fails to Shut OFF, Replacement Parts

NOTE: Always turn off and disconnect main supply wiring before servicing the unit.

4.Check connecting wire to the flame sensor. Verify that the flame sensor has not been damaged in any way.

5.Verify that the air supply is adequate. The air inlet screen or blower wheel may be restricted. Also, check the installation for proper ventilation. See AIR REQUIREMENTS.

6.Check the venting system for the correct sizing, excess or insufficient. See VENTING.

7.Check for a maximum inlet pressure of 11" Natural Gas

(2.74 kPa) W.C. and the manifold pressure as listed in Table 4: that is, for Natural Gas, 4.0" (0.996 kPa) W.C. Please note that the manifold pressure listed is the maximum value for the manifold pressure. Do not set the manifold pressure higher than the value shown for your heater in Table 4. Overfiring the heater will result in rough ignition and/or noisy operation.

8.Confirm that the air inlet screen (see Figures 7 & 8) is free of obstructions.

CAUTION

Do not reach into the burner housing or combustion chamber if the heater is still hot. Allow the heater to cool and always use gloves as the combustion chamber and the burner sleeve and housing can become very hot after operation. Overfiring is a dangerous condition that must be corrected immediately.

NOISY BURNER OPERATION

The exhaust of this unit produces some noise during ignition period. When combustion is too lean or too rich, start up noise will get worse. Check for flue gas CO2 reading, adjust gas valve manifold pressure if required to bring the flue gas CO2 to 9–9.5% level for natural gas, 10.75–11.25% for LP. This noise may be objectionable if the exhaust terminal is located too close to the opening of an occupied space. The noise may also be objectionable if the exhaust is located in the confined space between two buildings such as an alley or walkway. Since everyone's perception and tolerance for background noise varies, there is no standard recommendation. The best option when the noise is a concern is to fine-tune the air/ gas ratio of the combustion system or locate the exhaust as far away from any occupied spaces as practical.

GAS FAILS TO SHUT OFF

Check for defective gas valve or thermostat. If operation is incorrect, replace.

REPLACEMENT PARTS

Replacement parts may be ordered through A.O. Smith dealers, authorized servicers or distributors. Refer to the Yellow Pages for where to call or contact the A.O. Smith Water Products Company,

125Southeast Parkway, Franklin, TN 37068, 1-800-433-2545. When ordering parts be sure to state the quantity, part number and description of the items including the complete model and serial number as it appears on the product. Refer to the parts list for more information.

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