tekmar 421 Mixing Reset Module - Manual (Page 15)

15 of 20 © 2007 D 421 - 08/07
Boiler Enable Section E
If the 421 is one of many controls that can call for heat to
a single boiler or there is a boiler sequencer other than a
tekmar Stager (Boiler Control 264, 265, 268), operating
multiple boilers or multiple stages, then the boiler sensor
must be located on the return pipe of the boiler(s).
When the sensor is located on the return, the 421 provides
a boiler enable. The 421 no longer tries to control the
boiler supply water temperature directly, but allows another
operating control such as an aquastat to regulate the boiler
supply temperature.
When there is a requirement for heat from the 421 mixing
device, the 421 boiler contact closes to enable the boiler.
The boiler contact remains closed until heat is no longer
required.
When the boiler sensor is located on the boiler return, the
control is able to provide boiler return protection through the
use of a mixing device. This protects the boiler sustained
flue gas condensation and thermal shock.
To operate the control without a boiler sensor and prevent
the control from displaying an error message, set the boiler
sensor DIP switch to Return and power up the control
without the boiler sensor connected.
The control operation will be similar to that as having the
boiler sensor on the return except that boiler return protection
is no longer provided.
Pump Operation Section F
System Pump P1
The system pump P1 is switched on in the following
situation:
•
• There is a Mix Demand.
Variable Speed Pump
The variable speed injection pump output operates only when
there is a Mix Demand and the Mixing item in the Adjust
menu is set to variable speed injection pump (VAr).
Pump Exercising Section G
The system control will exercise all pumps and mixing valves every three days for ten seconds. If there is a heat demand,
the control will wait for the demand to be over before the start of exercising.