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(800) 865-5931

Closed Thur 11/26 - Sun 11/29, Reopen Mon 11/30 8am, CT

The AQ251 family 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 in-creased energy efficiency 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.


  • Use with AQ1000 2-wire polarity insensitive communicating thermostats.
  • Allows outdoor temperature to be displayed on all thermostats.
  • Intuitive programming interface and armchair programming (can be programmed at your desk and taken to the job site "ready-to-install")
  • Customizable control settings and schedules allow for greater level of control and comfort.
  • Central set-back schedules available.
  • 1-stage zoning.
  • Zoning Control for one zone as shipped; can be expanded to a total of 16 zones with AQ255 or AQ257 zoning expansion panels, and up to 64 zones by using AQ254 Add-a-Temperature expansion panel.
  • Outdoor temperature compensation (reset), or Load reset based on indoor temperature feedback.
  • Zone synchronization through Zone of Greatest Demand control.
  • Domestic hot water priority and priority override protection.
  • Line or low-voltage output for zoning equipment (pumps or valves).
  • Controls pumps or zone valves.
  • Boiler short cycling protection.
  • Boiler post purge.
  • Freeze protection.
  • Pump/valve exercise.
  • Automated test and purge feature for quick start-up and simple troubleshooting.
  • Integral 38 VA transformer with self resetting electronic fuse.
  • 2 hour power supply (super-capacitor) to retain day and time settings during power outage.
  • Non-volatile EPROM memory retains program settings during power outage.


The number of interior air handlers connected to the condensing unit. Typically one, two, or three zones.

Product Weight
5.7 lbs
16 1/2 Inches
3 3/8 Inches
8 Inches
120 Volts
60 Hz