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11
Operating information
General
How the water heater operates
The Shield water heater combines an advanced stainless steel
heat exchanger, electronic control module, and tank that
allows fully condensing operation. The blower pulls in air
and pushes flue products out of the heat exchanger and flue
piping.
The control module regulates blower speed to
control the water heater firing rate. The gas valve senses the
amount of air flowing into the water heater and allows only
the right amount of gas to flow. An internal pump circulates
the water between the tank and heater and mixes the
incoming water to provide maximum efficiency.
Temperature control
Modulation
The Shield water heater is capable of modulating its firing
rate from a minimum of 20% to a maximum of 100%. The
firing rate is dictated by the hot water draw and various other
temperature limitations.
Night setback
The controller may be programmed to reduce the tank set
point during a certain time each day. A start and stop time
can be programmed for each day of the week.
Flame current support
To prevent nuisance shutdowns when the water heater is
firing at minimum rates, the control will increase fan speed
when the flame signal drops too low.
Protection features
Outlet
temperature,
temperature rise limiting
The heat exchanger outlet temperature is monitored by the
heat exchanger outlet temperature sensor. When the heat
exchanger outlet temperature exceeds 190°F, the unit will
reduce the fan speed. If the heat exchanger outlet water
temperature exceeds 198°F the control will shut the unit
down until it cools off.
The control module monitors the flue temperature by a
sensor located in the flue exhaust. If the flue temperature
exceeds 215°F the control will reduce the maximum fan
speed. If the flue temperature exceeds 240°F the control will
shut the unit down. The unit will restart automatically once
the flue temperature drops 25°F and the minimum off time
has expired.
flue
temperature,
and
TM
The control monitors the temperature difference between the
heat exchanger inlet and the heat exchanger outlet sensors. If
this difference exceeds 25°F the control will reduce the fan speed.
If the temperature difference exceeds 30°F the control will shut
the unit down. The unit will restart automatically once the
temperature difference has dropped below 25°F and the
minimum off time has expired.
Freeze protection
DO NOT install the water heater in a room likely to freeze.
The following integral feature of the electronic control module
provides some protection for the water heater.
•
The
electronic
freeze-up protection as follows when the water heater
water temperature drops below 45°F:
•
Below 45°F, the internal pump operates constantly.
•
Below 37°F, the burner turns on.
•
The burner and pump will turn off if water
heater water temperature rises above 45°F.
This feature of the electronic control module
CAUTION
does not eliminate the possibility of freezing.
The installation must still use recognized
design, installation and maintenance practice
to prevent freeze potential for the water
heater.
Monitor external limits
Connections are provided on the connection board for external
limits. The electronic control module will shut off the burner
and inhibit relighting whenever an external limit opens.
Runtime and alarm outputs
The water heater provides dry contacts for indicating when the
water heater is running, and when it is unable to operate.
Error logging
The control will hold in memory the last 10 faults. The date and
time of the occurrence will be recorded as well. Only the 10
most current occurrences will be held in memory.
Installation & Service Manual
control
module
provides
47
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