User Guide

62
XII Operation
A. General Information
This boiler uses the microprocessor based Honeywell R7910B (“boiler control”) to manage all boiler functions including
amesupervisionandmodulation.Twosetpointor“target”boilersupplytemperaturesarestoredinthecontrol’smemory;
one for space heating (CH) and one for domestic hot water (DHW) production. If an outdoor temperature sensor is connected
to the boiler, and enabled, the space heating supply set point will automatically shift downward as the outdoor temperature
increases. For more information on this feature see the discussion on boiler water reset below. The control modulates the boiler
input by varying the fan speed. As the fan speed increases, so does the amount of gas drawn into the blower. As a result, a fairly
constant air-fuel ratio is maintained across all inputs. The control determines the input needed by looking at both current and
recent differences between the supply temperature and the set point temperature. As the supply temperature approaches the set
point temperature, the fan will slow down and the input will drop. The minimum input is approximately 1/5 of maximum input.
Thisboilercontrolalsomonitorsboilerreturnanduetemperatures.Inaddition,allothersafetycontrolsareconnectedintothe
R7910B. The R7910B uses inputs from all of these controls to either shut down the boiler when an unsafe condition exists or, in
some cases, to correct the problem. Finally, the R7910B manages up to three pumps:
  • Boilerpump
  • DHWpump
  • Systempump
Refer to the Piping Section for the location of these pumps.
Theboiler’sstatus,aswellasallsettings,areviewedandadjustedusingthecontrolpanel(“display”)onthefrontoftheboiler
(Figure 12.0). This display has three basic modes of operation:
1) User Mode - This is the default mode of operation for the control. By default, the display shows the home screen shown
in Figure 12.0. By pressing the LH or RH buttons at the bottom of the screen, it is possible to navigate to other User
Mode screens. See Figure 12.1 for a description of all User Mode screens.
2) Set-up Mode–Thismodeisusedtoadjustsettings,suchastargetwatertemperature.ToreachSet-upMode,holdboth
the Up and DWN keys for at least 3 seconds. All Set-up Mode screens are shown in Figure 12.2 and all settings are
described in more detail in Part B of this section.
3) Diagnostic Mode–DiagnosticModeisusedtoobtaininformationaboutrecentfaults,aswellastotemporarilylock
  theinputathighorlowreforthepurposeofrunningcombustiontests.ToreachDiagnosticMode,holdboththeLH
and RH keys for at least 3 seconds. All Diagnostic Mode screens are shown in Figure 12.7 and the use of these screens is
described both in this section and in Section XIV.
WARNING
This control panel is provided to enable a professional HVAC technician to set-up, check, and
troubleshoot this boiler. Attempts by others to make adjustments using this control panel could result
in death, personal injury, property damage, or unreliable operation.
B. Setting Up the Control
Enter Set-up Mode by pressing and holding both the UP and DWN buttons for at least 3s. The RH (Next) button advances
through the screens on this menu, saving any changes on the way. The LH (Done) button saves changes and returns to User Mode.
All Set-up Mode screens are shown in Figure 12.2. A description of each is as follows:
Temperature Units (S0)–Usedtoselecttemperatureunitsshownonthedisplay.
CH Set point (S1) - Target water temperature when the boiler is responding to a call for space heat. If outdoor reset is enabled, this
is the maximum target water temperature, regardless of outdoor temperature. See the Odr section below, as well as Figure 12.3,
for more information on outdoor reset.
Odr (S2)–Outdoorresetfunctionstatus.ThisscreenindicateswhethertheOdrfunctionisonoroffbyalternatelyashing“Odr”
and either “On” or “OFF”.