A) Pump Control On/Off Conditions (Only For Single And Easy-Link System) - A.O. Smith Water Heater 520 Direct Vent Indoor Service Manual

12-8. (A) Pump control ON/OFF Conditions (Only for single and Easy-link system)

To run circulation pumps efficiently and effectively, the 520 Indoor or 520 Outdoor offers four different
modes of pump control. The following table shows the pump control ON/OFF conditions for different
modes. To change pump control modes, see section 12-5 for dipswitch settings.
"Normal mode" and "Storage tank circulation mode"
There are no specific ON/OFF conditions for these two modes. The circulation pump will receive a
constant "ON" signal from the pump terminal on the computer board, and will run continuously.
"Re-circulation mode" and "Energy conserving re-circulation mode"
These functions enable the re-circulation pump to be controlled by the following conditions.
ON/OFF Conditions
Conditions that activate
the pump
Conditions that
deactivate the pump
*The computer records the inlet temperature and the flow rate of the pump during the final minute of
its previous operation when calculating the BTU requirement.
Re-circulation mode
The BTU requirement is more than
14,880 BTU/h*
OR
30 minutes have elapsed after
previous operation
5 minutes after activation, if the
computer detects a BTU
requirement of less than 14,880
BTU/h, the computer will stop the
pump in 90 seconds.
520 Indoor / 520 Outdoor Service Manual
Energy conserving re-circulation mode
Inlet water temperature is less than
95°F(35°C) and flow rate is less than
0.8GPM
20 minutes have elapsed after previous
operation
1 minute after activation, if the
computer detects a BTU requirement of
less than 14,880 BTU/h, the computer
will stop the pump in 75 seconds.
70
CONFIDENTIAL
Ver. 1.00
OR