tekmar 260 Boiler Control User Manual

Page 9

03/09

9 of 20

DHW Pump (DIP switch = DHW Pump)

DHW Pump is selected, the 260 assumes that the DHW pump provides adequate flow

through both the DHW tank heat exchanger, and the boiler. To provide heat to the DHW
tank, the 260 closes the

DHW Pmp / Vlv contact (9 and 10) and operates the boiler to

provide a sufficient boiler supply temperature to the DHW tank. If using a primary loop
with the DHW tank piped in primary / secondary, set the DIP switch to

DHW Valve.

DHW Valve (DIP switch = DHW Valve)

DHW Valve is selected and there is a DHW demand, the 260 closes the DHW Pmp /

Vlv contact (9 and 10) and the Boil P1 contact (7). The boiler pump provides flow through
the DHW’s heat exchanger once the DHW valve is opened. The 260 operates the boiler
to provide a sufficient boiler supply temperature to the DHW tank.

BOILER TARGET DURING DHW GENERATION (BOIL TARGET)

When the control receives a DHW demand, the BOIL TARGET is at least 180

°F (82°C).

DHW DURING UNOCCUPIED

If a DHW demand is received during an unoccupied (Night) period, the control can either continue operation of the DHW system as it
would during the occupied (Day) period, or the control can ignore a call for DHW as long as the control is in an unoccupied (Night)
mode. This option is selected using the

DHW during UnOcc DIP switch.

Section C2: DHW Priority

DHW PRIORITY

It is often desirable to limit or even stop the flow of heat to the heating system when the
DHW tank calls for heat. This allows for a faster recovery of the DHW tank. If DHW priority
is selected, the boiler pump (P1) is turned off on a call for DHW. This setting is available
only if DHW pump is selected as the DHW device (DIP switch =

DHW Pump). If a valve is

used as the DHW device, DHW priority can not be used. Caution should be taken to
ensure that the flow rate of the DHW pump is adequate for both the DHW tank and the
boiler, as this will be the only pump providing flow through the boiler. This feature is selected
using the

DHW Priority / Off DIP switch.

Note: If DHW Priority is selected with a DHW Valve, the control will display an error
message. Refer to the

Error Messages section at the back of this brochure.

DHW PRIORITY OVERRIDE

To prevent the building from cooling off too much, or the possibility of a potential freeze up
during DHW priority, the 260 limits the amount of time for DHW priority. As the outdoor air
temperature becomes colder, the length of time that the 260 provides DHW priority is
reduced. Once the allowed time for priority has elapsed, the 260 overrides the DHW priority
and operates DHW and heating simultaneously.

CONDITIONAL DHW PRIORITY

If the boiler supply temperature is maintained at or above the required temperature during DHW generation, this indicates that the
boiler has enough capacity for DHW and possibly heating as well. As long as the boiler supply temperature is maintained near its
target, DHW and heating occurs simultaneously.

DHW POST PURGE

After the DHW demand is removed, the 260 performs a purge on the boiler. The 260 shuts off the boiler and continues to operate
either the DHW pump, or the DHW valve and the boiler pump. This purges the residual heat from the boiler into the DHW tank. The
260 continues this purge for a maximum of four minutes or until the boiler supply water temperature drops below 160

°F (71°C). The

260 also stops the purge if the boiler supply temperature drops below the current BOIL TARGET temperature.

DHW

Valve

Pump

Outdoor Air Temperature

Increasing Air Temperature

Increasing T

ime

DHW priority demand time limit