Installation – tekmar 260 Boiler Control User Manual

Page 10

03/09

10 of 20

DHW MIXING PURGE

After DHW priority operation, the boiler is extremely hot. At the same time, the heating
zones may have cooled off considerably after being off for a period of time. To avoid
thermally shocking the boiler after DHW priority, the 260 shuts off the boiler, but continues
to operate the DHW while restarting the heating system. This allows some of the DHW
return water to mix with the cool return water from the zones and temper the boiler
return water.

Section C3: DHW with Low Temperature Boiler

If DHW is to be incorporated into a low temperature system such as a
radiant heating system, a mixing device is often installed to isolate the
high DHW supply temperature from the lower system temperature. If a
mixing device is not installed, high temperature water could be supplied
to the low temperature system while trying to satisfy the DHW demand.
This may result in damage to the low temperature heating system. The
260 is capable of providing DHW in such a system while ensuring that
the low temperature in the heating system does not exceed its allowed
maximum setting.

To prevent high temperature water from being introduced into the heating system, the boiler pump P1 must be turned off during a call
for DHW. To do this, the DHW device must be a DHW pump (DIP switch =

DHW Pump), DHW priority must be selected (DIP switch =

DHW Priority), and BOIL MIN must be set to OFF.

On a call for DHW, the 260 provides DHW priority by shutting off the boiler pump (P1) for a period of time. This time is based on the
outdoor air temperature as described in the DHW PRIORITY OVERRIDE section. However, if the DHW demand is not satisfied within
the allotted time, the boiler shuts off and the heat of the boiler is purged into the DHW tank.

Once the boiler supply temperature is sufficiently reduced, the DHW pump shuts off. The heating system is turned on for a period of
time to prevent the building from cooling off. After a period of heating, if the DHW demand is still present, the 260 shuts off the heating
system and provides heat to the DHW tank once again.

For correct operation, close attention must be paid to the mechanical layout of the system. When the 260 turns off the boiler pump
(P1), flow to the heating system must stop. If flow is not stopped, the temperature in the heating system can exceed the maximum
desired temperature, and can result in damage to the heating system.

Installation

CAUTION

Improper installation and operation of this control could result in damage to the equipment and possibly even personal injury. It is
your responsibility to ensure that this control is safely installed according to all applicable codes and standards. This electronic
control is not intended for use as a primary limit control. Other controls that are intended and certified as safety limits must be placed
into the control circuit.

STEP ONE

GETTING READY

Check the contents of this package. If any of the contents listed are missing or damaged, please contact your wholesaler or tekmar
sales representative for assistance.

Type 260 includes:

One Boiler Control 260, One Outdoor Sensor 070, One Universal Sensor 0

82, Data Brochures D 260,

D 070, D 001, Application Brochure A 260

Note: Carefully read the details of the Sequence of Operation to ensure that you have chosen the proper control for your application.

STEP TWO

MOUNTING THE BASE

Remove the control from its base by pressing down on the release clip in the wiring chamber, and sliding the control away from it. The
base is then mounted in accordance with the instructions in the Data Brochure D 001.

DHW