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VF BOILER SERVICE MANUAL
AOS WPC - Tech Training 64 of 72 Ashland City, TN © 2007
Servicing should only be performed by a Qualified Service Agent
BOILER CONTROLS (CONT)
INTERNAL TEMPERATURE CONTROLS (CONT)
Automatic High Limit - User Setting “Hi Limit”
The Automatic High Limit is a “local” EMC 5000 User Setting that can be adjusted through
the UIM (page 8).
The Automatic High Limit is a temperature limiting control, it reacts to temperatures sensed
at the Outlet Probe (page 62). It prevents the outlet water temperature from rising above the
programmed set point. If the temperature sensed at the Outlet Probe rises to the Automatic
High Limit set point the call for heat is deactivated. The boiler will go through a normal shut
down sequence with post purge cycling of the blower and pump. This IS NOT a Primary
System Control. The Automatic High Limit has a range of 90°F to 210°F for VW models and
90°F to 235°F for VB models (page 70).
Dead-band Operational Note: There is a fixed minimum dead-band between the
Automatic High Limit and the Operating Set Point of 20°F to prevent short cycling the boiler.
The Automatic High Limit can be programmed for more than 20°F above Operating Set
Point but not for less.
The Operating Set Point cannot be raised higher than 20°F below the Automatic High Limit
(Hi Limit) set point. Keep this in mind if the Operating Set Point seems stuck or will not allow
higher settings within it’s range. You may have to raise the Hi Limit set point first.
Automatic High Limit Differential - User Setting “Hi Limit Dif”
This Automatic High Limit Differential is a “local” EMC 5000 User Setting that can be
adjusted through the UIM (page 8). The Automatic High Limit Differential has a range of 1°F
to 50°F.
If the temperature sensed at the Outlet Probe (page 62) rises to the Automatic High Limit set
point, the EMC 5000 control system will deactivate the call for heat. The boiler will go
through a normal shut down sequence with post purge cycling of the blower and pump. The
call for heat will not be activated again until the temperature sensed at the Outlet Probe
drops below Automatic High Limit set point minus the Automatic High Limit Differential
setting.
IE: water temperature at the outlet of the boiler reaches 210°F, with an Automatic High Limit
setting of 210°F the boiler shuts down. With an Automatic High Limit Differential setting of
20°F the call for heat will not be activated again until the outlet temperature drops to 190°F.