Water Temperature Regulation; Control System - A.O. Smith VB-500 User Manual

WATER TEMPERATURE REGULATION

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
can scald and permanently injure you upon contact. Some people
are more likely to be permanently injured by hot water than others.
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 lowest possible temperature
setting that satisfies your hot water needs, a means such as a mixing
valve should 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. Follow the manufacturer's instructions
for installation of the valves. Before changing the thermostat setting
on the hot water system controller, see Table 1.
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 persons
increases the hazards to them. Never allow small 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.
Water Temperature
over 170°F (77°C)
160°F (71°C)
150°F (66°C)
140°F (60°C)
130°F (54°C)
120°F (49°C) or less
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
as follows:
• 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
120°F (49°C), adjustments on the water bypass are needed.
Please contact your A.o. Smith qualified service agent.

CONTROL SYSTEM

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
following printed circuit boards:
• 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 and contains the system fuses.
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.
There are several microcontrollers used on the boards. These
control the temperature and ignition control functions for
the boiler. Inherent in the design are the normal operating
10
Time to Produce 2nd & 3rd Degree
Burns on Adult Skin
Nearly instantaneous
About 1/2 second
About 1-1/2 seconds
less than 5 seconds
About 30 seconds
More than 5 minutes