Description 1-1
FlexFit – Linkageless Control – Revision 1.0
PREFERRED
UTILITIES MFG CORPORATION
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Section 1 – Description
Overview ........................................................................................................1-2
Features .........................................................................................................1-2
Safety Relay ..........................................................................................1-2
Field Selectable Flex Sequence Option ................................................1-3
Servo Checks ........................................................................................1-3
Automatic Fuel SSOV Leak Test ........................................................... 1-3
Lockout and Alarm History .................................................................... 1-3
MAF and PAF Safe Start Checks ..........................................................1-3
High Flue Gas Temperature Shutdown ................................................. 1-3
Fuel Selection and Flexibility .................................................................1-3
FD VSD to VSD Bypass Changeover ...................................................1-3
Pilot Test Hold .......................................................................................1-3
Flame Scanner/Relay ............................................................................ 1-3
Fuel/Air Position "Pacing Logic" ............................................................ 1-3
Tandem Oil/Gas Valve Servo ................................................................1-4
Oxygen Trim ..........................................................................................1-4
Firing Rate Setpoint and Control ...........................................................1-4
Call for Heat ...........................................................................................1-4
Domestic Hot Water Override ...............................................................1-4
Warm Standby Option ...........................................................................1-4
Cold Start WarmUp Cycle Option .........................................................1-4
Integrated Draft Control .........................................................................1-5
RS485 Modulating Lead/Lag Interface .................................................1-5
Burner Management System .........................................................................1-5
Description of BMS Sates .....................................................................1-8
Boot ...............................................................................................1-8
Standby ......................................................................................... 1-8
Safe Start Checks .........................................................................1-8
Prestart .........................................................................................1-8
Purge ............................................................................................1-8
Pilot Trial for Ignition (PTFI) .......................................................... 1-8
Main Trial for Ignition (MTFI) ........................................................1-8
Release to Modulate ............................................................... ...... 1-8
Assured Low Fire Cutout (ALFCO) Option ...................................1-8
Post Purge ....................................................................................1-8
Gas Valve Leak Test Option (Flex Sequence Option Only) .........1-9
Lockout .........................................................................................1-9
Interlock Groups ....................................................................................1-9
Call for Heat .................................................................................. 1-9
Recycling Limits ............................................................................ 1-9
Fuel Select .................................................................................... 1-9
Non-Recycling Limits ....................................................................1-9
Purging .........................................................................................1-9
Ignition ..........................................................................................1-9
False Flame ..................................................................................1-9
Flame Failure ................................................................................1-9
Fuel Valve Proof of Closure Switches (POCS) .............................1-9
Fan Speed ....................................................................................1-9
Combustion Control System ..........................................................................1-9
Parallel Positioning ..................................................................... 1-10
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