Cause of error code Hold 79

Outlet high limit

1. CH or DHW settings
2. CH or DHW pump problem
3. Incorrect “Outlet high limit” setting
4. Incorrect “Outlet high limit response” setting. 

Solution for error code Hold 79

1. Check if CH and/or DHW setpoint temperature plus off hysteresis exceed “High limit” setpoint – factory setting = 200°F (93°C). 
2. See "Inoperative CH or DHW pump" below.
3. Increase “Outlet high limit” setting; maximum setting = 200°F (93°C). 
4. Unless deemed unacceptable by local installation codes, the “Outlet high limit response” should be set to “recycle and hold” to prevent lockout.