9
NOTE:
(For Water Heaters) The maximum water temperature for lined vessels is 160°F, except for cement lined
vessels which can operate at 180°
F.
NOTE:
(For Hot Water Boiler) Outdoor reset (dual bulb) controllers are set at the temperature at which the
Boiler should operate when the outdoor temperature is 70°F (this outdoor reference temperature is adjustable
on most solid state controls; fixed on Honeywell T991B controllers). The reset ration (fixed on Honeywell T775J)
is the number of degrees the boiler control temperature will increase for a 1 degree decrease in outdoor
temperature.
5.1.1.3 Throttling Range
The throttling range is the number of degrees (or psi) the outlet water temperature (or steam pressure) must
change to drive the step controller from full-off to full-on.
For instance, if the controller is set at 160°F, and the throttling range is set for 10°F, the step controller will be
full-on at 165°F (1/2 of throttling range above setpoint). The more stable the load on the unit (from system
demands), the smaller the throttling range may be set.
5.1.2 High Limit (Temperature or Pressure
Manual reset limits should be set slightly higher than the automatic reset limits. For steam boilers, the manual
reset high limit should be set at lease 10% below the safety valve set pressure
.
5.1.3 Low Water Cutoffs
These cutoffs are always factory-set. If additional cutoffs are field-installed, the cut-offs should be at least three
inches above the highest heating element. Manual reset cutoffs should be set below automatic rest cutoffs
.
5.1.4 Low Limit Sensors (Temperature or Pressure)
Low limits should be set below the controller setting by at least the same margin as specified for high limits to
be above the controller setting
.
5.2 Operating Instructions
5.2.1
With the unit’s control power ON/OFF or ON/OFF/PREHEAT switch ‘OFF’, close the main power
switch(es
).
NOTE
: Units with shunt trip disconnects and remote 120-volt control power may require turning the control
power switch ‘ON’ and activating the 120-volt control power, before closing the main power switch(es).
5.2.2 Electric Door Interlocks
For units equipped with electric door interlocks, do not attempt to open electrical panel doors after the main
switch is closed. The lock tabs are mechanically restrained by the electric interlocks.
5.2.3
Switch all the ‘enable / disable’ pilot switches the ‘OFF’ position (toggle down).
5.2.4 120-Volt Power Source
If a separate 120-volt power source is provided, close it’s disconnect switch.
5.2.5
Turn the control power ON/OFF or ON/OFF/PREHEAT switch to ‘ON’.
5.2.6 Alarm and Reset Circuits
5.2.6.1
If the alarm sounds when the control switch is turned ‘ON’, depress the alarm silence button. Check
the unit to make certain that no limit condition exists by noting if the alarm pilot is illuminated. The alarm will
sound momentarily on some units when power is initially applied
.
5.2.6.2
Units with Manual Rest Button(s) may require resetting of the manual reset switch upon initial
application of power, and after the interruption or power or the trip-out of a limit control.
5.2.7 Sequencing of Elements Circuits
5.2.7.1
On units with step controls, the unit will always start with no steps energized.
5.2.7.2
As the steps begin cycling on, the LED’s on the step control (circuit board inside cabinet) will light up
one at a time, indicating that step control is operating properly.
NOTE:
The enable pilot lights or contractors will not be activated at this time since the ‘enable / disable’
switches are in the off position
.
