children to use a hot water tap, or to draw their own bath
water. Never leave a child or disabled person unattended in
a bathtub or shower.
The boiler should be located in an area that is inaccessible to
the general public.
TABLE 1. Risk of Scalds.
Over 170°F (77°C)
Time to Produce 2nd & 3rd
Degree Burns on Adult Skin
About 1/2 second
About 1-1/2 seconds
Less than 5 seconds
About 30 seconds
WATER TEMPERATURE REGULATION
120°F (49°C) or less
More than 5 minutes
SHOULD OVERHEATING OCCUR OR THE GAS SUPPLY FAIL
TO SHUT OFF, TURN OFF THE MAIN MANUAL GAS SHUTOFF
VALVE TO THE APPLIANCE.
The operating temperature of the boiler must be maintained
120°F (49°C) or higher inlet water temperature to the boiler.
20°F (11°C) differential between the boiler’s inlet and
outlet (e.g. 120°F [49°C] inlet, 140°F [60°C] outlet
minimum design temperatures).
If the inlet water temperature into the boiler is less than
20°F (49°C), adjustments on the water bypass are needed.
Please contact your A.O. Smith qualified service agent.
HOT WATER CAN SCALD: Boilers are intended to produce hot
water. Water heated to a temperature which will satisfy space
heating, clothes washing, dish washing and other sanitizing needs
The EMC modulation control system is a fully integrated, state of
the art electronic control system. It consists of sensors, output
devices, a power switch, a 24VAC transformer, wiring, and the
can scald and permanently injure you upon contact. Some people following printed circuit boards:
are more likely to be permanently injured by hot water than oth-
ers. These include the elderly, children, the infirm or physically/
mentally disabled. If anyone using hot water in your home fits
into one of theses groups or if there is a local code or state law
requiring a specific temperature water at the hot water tap, then
you must take special precautions. In addition to using the low-
est possible temperature setting that satisfies your hot water
needs, a means such as a mixing valve shall be used at the hot
water taps used by these people or at the hot water supply tank.
Mixing valves are available at plumbing supply or hardware stores. and contains the system fuses.
Follow the manufacturer’s instructions for installation of the valves.
Before changing the thermostat setting on the hot water system
controller, see Table 1.
Modulation Control Board (MCB)
Power Distribution Board (PDB)
User Interface Module (UIM)
The MCB contains circuitry for both master control and flame
control. Dip switches on the MCB are used to configure the system.
The User Interface Module (UIM) communicates with the user
through a set of touch pads and a 4-line, 20-character LCD display.
The PDB provides connection points for input power, the water
pump, and the transformer. It also distributes power to the system
The MCB also contains an external communications system to allow
for connection to a PC, a modem, an EMS system, or something
similar. Through this connection, multiple boilers can also be
linked together. CAUTION: The internal communications
cables should never be connected to the external
communications connectors, and vice-versa.
Hot water temperatures required for automatic dishwasher
and laundry use can cause scald burns resulting in serious
personal injury and/or death. The temperature at which injury
occurs varies with the person's age and time of exposure.
The slower response time of children, aged or disabled control the temperature and ignition control functions for the
persons increases the hazards to them. Never allow small boiler. Inherent in the design are the normal operating
There are several microcontrollers used on the boards. These