A.O. Smith DB/DW-720-1810 warranty Features, Safety Relief Valves

FEATURES

IMPORTANT

Only qualified personnel shall perform the initial firing of the heater. At this time the user should not hesitate to ask the individual any questions regarding the operation and maintenance of the unit.

Lighting and Operating instructions are included at the rear of this manual. By using this checklist the user may be able to make minor operational adjustments and save unnecessary service calls. However, the user should not attempt repairs which are not listed under the USER column.

SAFETY RELIEF VALVES

Your local code authority may have other specific relief valve requirements not covered below.

WARNING

THE PURPOSE OF A SAFETY RELIEF VALVE IS TO AVOID EXCESSIVE PRESSURE WHICH MAY CAUSE TANK EXPLOSION, SYSTEM OR BOILER DAMAGE.

TO AVOID WATER DAMAGE A DRAIN LINE MUST BE CONNECTED TO A SAFETY RELIEF VALVE TO DIRECT DISCHARGE TO A SAFE LOCATION. A DRAIN LINE MUST NOT BE REDUCED FROM THE SIZE OF THE VALVE OUTLET AND IT MUST NOT CONTAIN ANY VALVES BETWEEN THE BOILER AND THE RELIEF VALVE OR THE RELIEF VALVE AND THE DRAIN EXIT. IN ADDITION, THERE SHOULD NOT BE ANY RESTRICTIONS IN A DRAIN LINE NOR SHOULD IT BE ROUTED THROUGH AREAS WHERE FREEZING CONDITIONS MIGHT OCCUR. DO NOT THREAD OR CAP THE DRAIN LINE EXIT. RESTRICTING OR BLOCKING A DRAIN LINE WILL DEFEAT THE PURPOSE OF THE RELIEF VALVE AND MAY CREATE AN UNSAFE CONDITION. INSTALL A DRAIN LINE WITH A DOWNWARD SLOPE SUCH THAT IT NATURALLY DRAINS ITSELF.

If any safety relief valve is replaced, the replacement valve must comply with the latest version of the ASME Boiler and Pressure Vessel Code, Section IV (“HEATING BOILERS”). Select a relief valve with a discharge rating NOT less than the boiler input, and a set pressure NOT exceeding the working pressure of any component in the system.

An ASME rated temperature and pressure relief valve must be installed on each and every water storage tank in a hot water supply system.

The storage tank temperature and pressure relief valve must comply with the applicable construction provisions of the Standard for Relief Valves and Automatic Gas Shutoff Devices for Hot Water Supply Systems, ANSI Z21 or CAN/CSA-B149.1 (latest edition). The valve must be of the automatic reset type and not embody a single-use type fusible plug, cartridge or linkage.

ELECTRONIC INTERMITTENT PILOT

IGNITION CONTROL

ALL MODELS - The solid state ignition control, fig. 2, ignites the pilot burner gas by creating a spark at the pilot assembly. Pilot gas is ignited and burns during each running cycle. The main burner

and pilot gases are cut off during the “OFF” cycle. Pilot gas ignition is proven by the pilot sensor. Main burner ignition will not occur if the pilot sensor does not first sense pilot ignition.

FIGURE 2

On natural gas models the igniter control continues to operate (creating a spark) until the pilot burner is ignited or the ignition system shuts down. Shut down occurs automatically if the pilot burner does not ignite within 15 seconds. The unit then waits for

(5) minutes and retries ignition (standard models).

The electronic intermittent pilot ignition control and the 100% lockout control are non-adjustable devices.

(See troubleshooting steps on page 40). If pilot is not lit and sensed within the flame establishing timing for each module, the appliance will shut down.

MANUAL RESET HIGH TEMPERATURE

SAFETY LIMIT CONTROL

This device senses water temperature in the boiler. When water temperature exceeds dial setting, power to main gas valve is interrupted and the boiler is shut down.

HOT WATER SUPPLY - Manual reset - factory set at 210°F (100°C). Water temperature must drop at least 20°F (11°C) before reset is possible.

HYDRONIC HEATING - Manual reset - factory set at 250°F (121°C). Water temperature must drop at least 20°F (11°C) before reset is possible.

Single stage and modulating units use a combined control as shown in fig. 4.

Dual stage models are equipped with a limit like one shown in figure 3.

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