A.O. Smith VB/VW- 750 Water Temperature Limit Controls, ON/OFF Switch, Circulating Pump

Water Temperature Limit Controls

The “V(B/W)” models incorporate an outlet water probe consisting of two limit controls:

1.A Manual Reset High limit control that can be set as high as either

210°F (99°C) or 235°F (113°C), depending on the application.

2.A fixed manual high limit, factory set at 244°F (118°C). If the manual reset should open due to high temperature, the gas valves will close and unit will go into lockout. If lockout occurs, push the SELECTION button on UIM to restart boiler.

ON/OFF Switch

The ON/OFF Switch is a single-pole, single­-throw rocker switch. This switch provides­ 120V from the line source to the boiler.

Circulating Pump

HOT WATER SUPPLY BOILER-VW, the circulating­ pump is integral to the VW models. This pump has been lubricated­ at the factory, and future lubrication­ should be in accordance with the motor manufacturer’s instructions provided as a supplement to this manual.

HOT WATER HEATING BOILERS-VB, the cir­culating pump is NOT provided on standard models (optional) and must be obtained and installed in the field.

NOTE: If a system pump is to be installed on a VB model, the maximum rating of pump motor must not exceed 1 hp.

Temperature Probes

INLET / REMOTE

TEMPERATURE

PROBE

OUTLET

TEMPERATURE

PROBE

FIGURE 7. Remote PROBE INSTALLATION.

Temperature probes are 3/4 inch male NPT threaded immersion probes, see Figure 7. Temperature probes have embedded temperature sensors (thermistors). The boiler’s control system monitors these sensors to determine water temperature at various points in the system.

INLET AND OUTLET TEMPERATURE PROBES

All VF boilers have one Inlet and one Outlet Temperature Probe factory installed in the top of the heat exchanger to monitor the water temperature entering and leaving the boiler. The Inlet Probe is a temperature sensor only and has two leads. The Outlet probe also contains the manual reset high temperature limit switch and has four leads. The control system displays the Inlet and Outlet water temperatures sensed from these two probes on the default Temperatures screen.

REMOTE TEMPERATURE PROBE

All VF boilers are supplied from the factory with a Remote Temperature Probe. The supplied Remote Temperature Probe is used to control system water temperature for a single boiler in a domestic hot water storage tank or in the return line from a primary/secondary hydronic heating system. Use of the Remote

Temperature Probe allows a boiler to sense the actual water temperature inside the storage tank or hydronic heating loop. The boiler will modulate its firing rate in response to the actual system temperature and load conditions. The control system displays the temperature sensed from the Remote Temperature Probe as the “Tank” temperature on the default Temperatures screen.

QUAD THERMISTOR PROBE

When connecting up to 4 boilers to a single storage tank or one primary/secondary hydronic heating system the optional Quad Thermistor Probe should be used. The Quad Thermistor Probe is a remote temperature probe with four temperature sensors embedded in one device. The Quad Thermistor Probe allows up to 4 boilers to sense system temperature from same point in the system. Use of the Quad Thermistor Probe will allow each connected boiler to individually sense actual water temperature in the storage tank or hydronic heating loop. The temperatures sensed from each of the four temperature

sensor circuits in a Quad Thermistor Probe are shown as “Tank”

temperature on each boiler’s default Temperatures screen.

NOTE: See the Field Wiring, Remote Temperature Probe Installation and the Primary System Control sections of this manual for operating and installation instructions.

Low Water Cutoff (Optional)

If boiler is installed above radiation level, a Low Water Cutoff Device must be installed in boiler outlet at time of installation or, order pre-installed from the factory. If low water detection is required by authorities having jurisdiction, a low water cutoff switch should be installed in the boiler outlet water line. The switch should receive periodic (every six months) inspection to assure proper operation.

Pressure Relief Valve

An ASME rated pressure relief valve is furnished with the boiler. Never operate the boiler if it is not filled with water and a properly sized pressure relief valve is not installed.

The pressure rating of the relief valve should be equal to or less than the rated pressure capacity of any component in the system including the boiler. Should the valve need to be replaced, call the toll free phone number listed on the back of this manual for further technical assistance.

Explosion Hazard

Relief Valve must comply with ASME code.

Properly sized Relief Valve must be installed.

Can result in overheating and excessive tank pressure.

Can cause serious injury or death.

A discharge pipe from the relief valve should terminate at an adequate floor drain. Do not thread, plug, or cap the end of drain line.

CAUTION

Water Damage Hazard

•Pressure Relief Valve discharge pipe must terminate at adequate drain.

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