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USER OPERATION AND MAINTENANCE

69-1979-04

AQUATROL Zone Synchronizing 

Boiler Reset Controls

AQ251

APPLICATION

The AQ251 series of AQUATROL® Boiler Reset Controls 

provides simplified, energy-efficient outdoor temperature 

compensated control of single-temperature, residential 

hydronic heating systems. The AQ251 easily converts a single 

zone heating system into a room-by-room comfort control 

system, or upgrades a basic, relay-logic zoning system to 

intelligent “Zone of Greatest Demand” control with outdoor 

reset for increased energy efficiency and with reduced boiler 

cycling. 

AQ251 boiler controls can ensure ample supply of hot water 

for both space heating and priority generation of domestic hot 

water for bathing, dishes and laundry.

When AQ1000 communicating thermostats are used with the 

AQ251 Zoning Modules, they can use the same wiring as 

existing thermostats. Night setback operation can be 

programmed from the AQ251 panel. Thanks to the network 

communication capability of the AQ251 controls, AQ1000 

thermostats in the home can display the actual outdoor 

temperature when an outdoor sensor is connected to the 

AQ251 Control Panel.

WARNING

Only trained, experienced, licensed service 

technicians should service this Control Panel. The 

front cover of the AQ251 Control Panel should not 

be removed, as this will expose the user to 

potentially dangerous line voltage (120V) 

electricity.

Congratulations!

The AQUATROL AQ251 installed on your heating system is 

the most powerful, yet user-friendly hydronic heating control 

system available on the market for residential and light 

commercial installations.

This instruction sheet contains all the information you need to 

program the comfort settings of the AQ251 and to customize 

its operation for your home or business. For detailed 

information on the operation of this control, please consult the 

trained hydronic heating professional that installed the AQ251 

control.

CONTENTS

Application ........................................................................

1

Familiarization with Control  ..............................................

2

User Interface   ..................................................................

2

LCD Display Panel Layout ................................................

3

Programming Instructions .................................................

4

Troubleshooting ................................................................

6

System Status and Error Codes  .......................................

6

User Menu Structure .........................................................

8

This AQUATROL AQ251 Control Panel was installed by a trained hydronic heating contractor.

To service this product, or for any questions relating to its installation, please contact:

Installing contractor: ________________________________________________________

Address: __________________________________________________________________

Phone: (_______) __________________________________________________________

Summary of Contents for AQ251

Page 1: ... experienced licensed service technicians should service this Control Panel The front cover of the AQ251 Control Panel should not be removed as this will expose the user to potentially dangerous line voltage 120V electricity Congratulations The AQUATROL AQ251 installed on your heating system is the most powerful yet user friendly hydronic heating control system available on the market for resident...

Page 2: ...umber the displayed value will decrease increase by pressing these buttons When holding the or button for more than a second the values automatically decrease increase at a faster pace similar to setting the time on a digital clock radio If the menu item is an option pressing these buttons scrolls through the list of available options one at a time Fig 1 LCD Dot Matrix Display Layout Model Functio...

Page 3: ...tback schedule you must use the or button to change the time 2 The OK button when pressed defaults the time setting to midnight If the active menu item leads to a further sub menu pressing the OK button displays the sub menu options on the LCD Scroll through this sub menu to position the indicator arrow beside the desired menu item to input or modify Choose one of the options provided or input the...

Page 4: ...for both the AQ251 control s LCD and the zone thermostats The time display in 12 hour e g 7 00 PM or 24 hour format e g 19 00 Date and time of day allows building owner to reset day and time of day in the event of a power outage of more than 4 hours refer to Troubleshooting section The Home Page display view Simple or Detail The factory default is Detail The LCD Backlight illuminated permanently O...

Page 5: ...ur programs have been set select the COPY TO ALL DAYS option This displays the prompt COPY TO ALL DAYS ARE YOU SURE Select Yes by positioning the indicator arrow at YES and press the OK button Next the same list of days as EDIT DAILY described in step 1 displays except that all days now show the times for the WAKE LEAVE RETRN and SLEEP programs that you set in the EDIT ALL DAYS menu If you do not ...

Page 6: ...ve and the minimum ON time has not yet elapsed AUX IN EM SHUT n a Auxiliary Input s Emergency Shut Down is active BOILER EM SHUT Boiler is disabled because the AQ251 is in Emergency Shut Down mode FRZ PROT Boiler freeze protection activated Communication between Control Module and Zoning Module has been lost for more than 1 minute or Boiler supply temperature is less than 50 F 10 C HEAT DHW Boiler...

Page 7: ...ntractor quickly identify the lost zone and fix its wiring to re establish communication with the Control Module NO RETURN PROBE n a No return sensor connected or it is defective NO SUPPLY PROBE n a No supply sensor connected or it is defective SHORT CYCLE PROT n a There is a call for heat but less than two minutes have elapsed since the last firing of the boiler prevents short cycling VALVE INIT ...

Page 8: ...CLE PROT VALVE INIT WATER READY WWSD ACTIVE SYSTEM STATUS 1 ZONE A 1 ROOM TEMP FLOOR TEMP SETPOINT 70 FLOOR SETPT 70 HEAT COOL STATUS SETBACK 7 SETPOINT MAX 100 SETPOINT MIN 41 FLOOR LIM HI 100 FLOOR LIM LO 41 SETPOINT VACANCY HEAT 41 SETPOINT VACANCY COOL 100 CHANGEOVER 2 KEYBOARD UNLOCK ZONE SETTINGS All or Single 2 ARE YOU SURE NO YES MON WAKE 6 00A MON LEAVE 8 00A MON RETRN 4 30P MON SLEEP 10 ...

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