tekmar 374 Universal Reset Control - Manual (Page 6)

© 2009 D 374 - 03/09 6 of 36
EXERCISING
The control has a built-in exercising feature, which ensures that each pump or valve is operated at least once every 3 days. If
a pump has not been operated at least once every 3 days, the control turns on the output for 10 seconds. This minimizes the
possibility of the pump seizing during a long period of inactivity. While the control is exercising, the
Test LED flashes quickly.
Note: The exercising function does not work if power to the control or pumps is disconnected.
BOILER PROTECTION
The control is capable of providing boiler protection from cold mixing system return temperatures. The control protects the boilers
by either reducing the variable speed injection pump speeds or by closing the four way valves. This limits the amount of cool return
water to the boiler and allows the boiler water temperature to recover.
BOILER DEMAND
A boiler demand is required in order for the control to provide heat to the heating system.
A boiler demand is generated by applying a voltage between 24 and 230 V (ac) across the
Boil Dem and Com Dem terminals (30 and 31). Once voltage is applied, the Boiler Demand
pointer is displayed in the LCD. If the control is not in Warm Weather Shut Down (
WWSD),
the control closes the primary pump contact. The control calculates a boiler target supply
temperature based on the outdoor air temperature and the boiler characterized heating
curve settings. The control then fires the boiler(s), if required, to maintain the boiler target
supply temperature.
BOILER SUPPLY SENSOR
The boiler sensor can be located on the boiler supply if the 374 is the only control that is
operating the boiler(s). When the
Return / Supply DIP switch is set to Supply, the control
determines the required operating temperature for the boiler supply and operates the Stage 1
and Stage 2 contacts in order to maintain the correct boiler supply water temperature.
30 31
Boil
Dem
Com
Dem
24 to 230 V (ac)
Boiler
Sensor
PRIMARY PUMP OPERATION
The primary pump operates when the control receives boiler, mix 1 or
mix 2 demands and is not in Warm Weather Shut Down (WWSD). The
primary pump will operate in DHW MODES 3 and 4 when a DHW demand
is present. The primary pump also operates in Setpoint MODE 3 during
setpoint demands.
Primary Pump Purge
After any demand that operates the primary pump is removed, the control
continues to operate the primary pump for an additional 20 seconds.
Section B1
Boiler
Reset
Section B: Boiler Operation
Section B1: Boiler Reset
Section B2
Boiler
Enable