AquaSmart Freeze Resistance Operation

AquaSmart Freeze ResBeckett has received many questions about the “FREEZE RES” or freeze resistance feature built into all AquaSmart Controls. This bulletin provides an overview of the freeze resistance function. The AquaSmart is designed for use only in hot water systems.


The purpose of the Freeze Resistance programming in the AquaSmart control is to provide additional protection against freeze up of the heating pipes by circulating water through the pipes if the AquaSmart control, burner, or ignition control lockout. The Freeze Resistance mode is activated when:

  1. The AquaSmart control has been in lockout for 3 hours, or
  2. When a call for heat from the space has been active for 3 hours continuously, or
  3. When the low limit function has been active for 3 hours continuously.

Circulating water may help prevent pipes from freezing if the burner fails to operate properly or if burner operation fails to raise the temperature in the boiler above the low limit setting.

Freeze Resistance Operation

The freeze resistance timer is started when there is a call for heat, when the low limit energizes or when the AquaSmart control enters a lockout. If the timer reaches 3 hours (180 minutes), the freeze resistance mode is activated. In the earliest AquaSmart controls, the freeze resistance activated after 1 hour instead of the current 3 hours. When the freeze resistance mode is activated, the letters “FREEZE RES” appear on the display screen. ZC is energized to allow zones to call for heat (even if the boiler water temperature is
below the low limit setting). B1 will be energized unless the AquaSmart control is in lockout. The circulator will be controlled as described in the paragraph below.

When the AquaSmart enters the “Freeze Res” mode, the circulator control logic will take one of the actions below:

  1. If the circulator is already running, it will continue to run.
  2. If there is an active call for heat from the space or zones, the circulator (C1) will be energized.
  3. If there is no call for heat from the space or zones, the circulator will not be energized. This protects the pump against trying to circulate water through a zoned system when all the zones are closed. “Freeze Res” will still appear on the screen.

The freeze resistance timer will reset automatically when any of these conditions are met:

  1. The call for heat or low limit is satisfied.
  2. The high limit opens.
  3. Power is interrupted.
  4. The AquaSmart lockout condition is cleared.

To manually reset the freeze resistance timer, turn off the thermostat for 10 seconds or turn off the power to the control for 10 seconds, then restore power to the control. “Freeze Res” will disappear from the screen if the timer has been successfully reset.

“Freeze Res” is not an error code and does not lockout the burner or override the call for heat.
“Freeze Res” notifies the service technician that the AquaSmart has been in lockout for at least 3 hours or that there has been a continuous call for heat for at least 3 hours. “Freeze Res” is not an error code and does not mean the control has failed or should automatically be replaced. The service technician still needs to follow troubleshooting procedures to determine if the system is operating properly or if there is an issue preventing burner operation. If the AquaSmart is in lockout, it will prevent burner operation.

AquaSmart Lockout and Freeze Resistance
If the AquaSmart control has been in lockout for 3 hours, the display will alternate between the “Freeze Res” screen and the lockout screen every 5 seconds. When the AquaSmart is in lockout, it will not power the B1 (burner) terminal.

The Display Screen will alternate between “Freeze Res” and “Lockout” when both conditions exist at the same time.

AquaSmart Lockout codes

WTR: 75F

Removing power from the control will reset the freeze resistance timer but will not remove the control from lockout if the cause of the lockout remains (allow 20 seconds after power up to clear lockout).

“Freeze Res” does not always mean there is a problem with the heating system.
In extremely cold weather or following a night setback, an active call for heat could easily last for 3 hours. High mass boilers, radiant heat applications, systems with long pipe runs, a sudden drop in outdoor temperature (especially on outdoor reset applications), or even a system well matched to the heating load could result in long call for heat cycles. In these cases, the “Freeze Res” message would appear, but as long as the circulator was running, the freeze protection program would have no impact on the AquaSmart operation. The ‘Freeze Res” message will disappear when the call for heat is satisfied.

Reasons “Freeze Res” may be activated (after 3 hours)

Reason Possible causes
Long Call for Heat High mass boilers, seasonal start up, recovery from night setback, extended pipe runs, circulator or piping issues, thermostat issues, large temperature drop with outdoor reset controls, radiant heat applications.
Primary Control Lockout Gas ignition control or oil primary control in lockout, igniter issues, flame sense issues, fuel issues.
AquaSmart Lockout AquaSmart controls locks out on Sensor Error, Self-Check Error or Low Water Lockout, lockout screen will alternate with “Freeze Res” on display.
Wiring/Damper Issues Poor connection to AquaSmart or burner control, poor connection in the LWCO circuit (Lockout Low Water), on gas units with damper – poor connection in damper circuit, damper fails to open completely or end switch fails to make when damper opens.