Crown Boiler 24-04 用户手册

50

  TEST CONTROLS

 

All controls must be checked prior to putting the boiler 

in service.

1.  CHECK OPERATING CONTROL OPERATION.

  Raise and lower operating control setting as required 

to start and stop burner.

2.  CHECK OPERATION OF HIGH LIMIT 

CONTROL —

  Jumper Operating Control Terminals.  Allow burner 

to operate until shutdown by limit.  Installation is 

not considered complete until this check has been 

made. REMOVE JUMPER.

3.  CHECK LOW WATER CUTOFF control with water 

level at normal water line (see Figure 1).  Raise 

operating control setting to allow burner to operate.  

Open boiler drain to allow water level to drop to 

bottom of sight glass until burner operation is shut 

down by low water cutoff.

  Close boiler drain and refill to normal water line.  

Burner should automatically restart during fill.  

RESET OPERATING CONTROL.

both the boiler circulator and the diverting valve 

during periods of dormant activity provided power 

is supplied to the control.

  DIVERTING VALVE ACTUATOR - A 3-way 

diverting valve is used to control the temperature of 

the water returning to the boiler. Proper operation 

is required to protect the boiler from thermal shock 

and sustained condensate production.  Confirm the 

operation of the valve as shown above.  See Figures 39a 

and 39b.

  BOILER OPERATING AQUASTAT – The operating 

aquastat, L4006A, can be found on the front of the 

boiler, to the right of the temperature/pressure gauge.  

The operating aquastat should be set to the designed 

supply temperature, typically 180ºF.  The operating 

aquastat set point, the RTC MIX TARGET or the RTC 

MIX DESGN, should be set to the same value for 

20°F ∆T applications.  In 40°F ∆T applications, the 

operating aquastat (L4006A) must be set 20°F higher 

than the MIX TARGET and MIX DESIGN .  Under 

no circumstances should the operating aquastat be set 

below 135ºF plus (+) the designed boiler temperature 

drop, ∆T (ºF).  
  Example: if the flow rate through the boiler 

corresponds to a 20ºF ∆T design, the operating 

aquastat cannot be set lower than 135 + 20 = 155ºF.  

 

In reality, most systems are designed for a 180ºF supply 

water and 160ºF return water.  The accuracy of the 

operating aquastat is less than the RTC accuracy, often 

requiring the operating aquastat temperature to be 

bumped upward a few degrees.

  BOILER HIGH LIMIT AQUASTAT – If used, the 

high limit aquastat, L4006E, can be found on the front 

of the boiler, to the left of the temperature/pressure 

gauge.  The high limit aquastat can be identified with a 

red manual reset button.  Ideally, the high limit aquastat 

should be set 10 -15°F above the RTC MIX MAX 

setting, when the outdoor reset feature is selected.  

Typically, this is set between 200ºF and 220ºF.  The 

temperature must be set below the lowest permissible 

temperature for any system related component affected 

by boiler supply water.  Under no circumstances can the 

high limit aquastat be set higher than 250ºF.

  BOILER MODULATING CONTROL – Various 

controls are used to modulate burner firing rates.  

No attempt will be made to cover every possibility, 

however a general outline will be given.  

 

Most modulation controls require the entry of a 

boiler temperature identifying boiler operation at the 

maximum firing rate.  A boiler operating temperature 

below that will also generate a full firing rate.  When a 

boiler heat demand is generated the unit will initiate at 

either a low or high fire rate and quickly ramp up to the 

high fire rate.  The unit will continue to fire at the high 

fire rate until the boiler high fire modulating limit is 

reached.

 

Many modulation controls require the entry of a burner 

off or low fire setting.  The burner will modulate 

between the high fire and low fire rate based on the 

absolute boiler temperature as well as the rate of change 

in boiler temperature.

 

If using a T991 Proportional Control or a similar 

modulating device in a traditional hydronic system, 

the minimum setting shall be the sum of the designed 

heating system return temperature + boiler ∆T + 10°F.
  Example:  System Supply   180°F
     System Return     160°F
     System ∆T  

 20°F

     Boiler ∆T    

 40°F

  Min. Setting = 160°F + 40°F + 10°F
          = 210°F
  *NOTE:  A higher flow through the boiler, achieving 

a 20°F ∆T would lower the minimum to 190°F.

 

If using the same control in a system where the 

designed return is less than 135°F, then the minimum 

becomes:

 

 

135°F + Boiler ∆T + 10°F