A.O. Smith 200M, 225M, HW-120M, 160M Features, Automatic GAS Shutoff Control, Thermal Balancer

FEATURES

TABLE 4.

Control Device		Factory Setting	Field Adjustment
		1950F (90.5°C) cut out temp.
Heater Automatic Gas Shutoff Control	Fixed	1900F (87.7°C) cut in temp.	Non-adjustable
		2500F (121°C) cut out temp.
Heater Protector Switch	Fixed	2000F (93.3°C) cut in temp.	Non-adjustable
Tank Temperature Control	Field Supplied and Installed		Adjust to Requirements
Safety Flow Switch	See Table 1		Field Adjustable

AUTOMATIC GAS SHUTOFF CONTROL

The automatic gas shutoff control, fig. 1, is an automatic safety device which activates at a water temperature of approximately 1950F (90.5°C). This limits the water outlet temperature to a maximum of 2000F (87.7°C).

The device is wired in series with the gas valve. The control will automatically reset when the water temperature cools to approximately 190oF (87.7°C).

Should the automatic gas shutoff control activate during a heating cycle, the heater’s gas valve will close; extinguishing the main burners. The pilot burner will also be extinguished. The circulating pump will continue operating as long as the storage tank thermostat continues to “call for heat”. When the water temperature in the heater drops to 1800F (82.2°C) or below the control module will begin an ignition cycle which will relight the pilot burner and main burners. Re-ignition of the main burners will occur if the storage tank thermostat continues to call for heat. Otherwise, the normal operating cycle will resume on the thermostat’s next call for heat.

AUTOMATIC GAS SHUTOFF CONTROL

FIGURE 1

PROTECTOR SWITCH (Coil High Limit)

This heater is equipped with a manually reset protector switch, Figure 2, located under the small cover on the side of the jacket. This device provides positive shutdown of the heater in the event of heater or system malfunction. Should the surface temperature of the copper tubing heat exchanger reach 2500F (121.1°C), the protector switch will activate. The gas valve will close, and the pilot and main burners will be extinguished. To resume heater operation, the protector switch must be manually reset (remove the protector switch cover and push the reset button) after the coil surface temperature cools to less than 2000F(93.3°C).

FIGURE 2

DO NOT RESET THIS SWITCH WITHOUT PERFORMING THE SYSTEM CHECKS OUTLINED UNDER PROTECTOR SWITCH IN THE SERVICE INFORMATION SECTION. ALSO, SEE CHART ONE UNDER THE CHECKOUT SECTION. IF NECESSARY, CALL A QUALIFIED SERVICEMAN. Once the cause of the protector switch activation has been determined and corrected, it will be necessary to restart the heater following the LIGHTING AND OPERATING instructions.

THERMAL BALANCER

The thermal balancer (standard on Models HW-200M and HW-225M, optional on Models HW-120M and HW-160M) is a snap-acting single-pole thermal relay used only on Cer-Temp 80 Recovery systems. It gives immediate pump start but delay of pump shutoff for approximately 2 minutes. Residual heat in the heat exchanger is then recovered after shutdown. This improves efficiency and balances heater temperature with tank temperature at shutdown.

INTERMITTENT IGNITION CONTROL MODULE

The Honeywell S-8600 control module contain the electronic components of the system and also serve as a central wiring system for the controls mounted on the heater. The control module performs the following functions:

1.Checks for safe-start by sensing for a flame or false flame condition on start-up.

2.Generates a potential of 15,000 volts for spark ignition of the pilot burner.

3.Opens the pilot valve.

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