Tekmar DHW Control 252 Manual Download Page 7

Page: 7 / 12

Step Six

Essential control settings

To obtain the best operation from a reset control, it is important to measure the system supply temperature as accurately
as possible. Whenever the control receives a heat demand signal, the system pump must be operated to maintain
continuous water flow past the supply temperature sensor.

For specific application details refer to Application Brochure A 252.
A more detailed technical description of the effect of control settings on overall system operation is described in the tekmar Essay E 002.

Test the power supply

Make sure exposed wiring or bare terminals are not in contact with any other wires or grounded surfaces. Turn on the power to the
transformer and use an AC voltmeter to measure the voltage between terminals

C — R (5 and 6). 22 to 26 Volts AC should be measured

at these terminals.

Test the powered inputs

If an external Heat Demand signal is used, power up the Heat Demand circuit and supply a Heat Demand signal to the control. Use

AC voltmeter to measure the voltage between terminals

Heat Dem — Heat Dem (1 and 2). 22 to 26 Volts AC should be

measured at

these terminals.

If a DHW Demand signal is used, power up the DHW Demand circuit and supply a DHW Demand signal to the control. Use an AC
voltmeter to measure the voltage between terminals

DHW Dem — DHW Dem (3 and 4). 22 to 26 Volts AC should be measured at these

terminals.

If a System Pump circuit is connected to the

Sys Pmp — Sys Pmp (7 and 8) terminals; make sure power to the circuit is off and install

a jumper in the terminal plug between terminals 7 and 8. When the circuit is powered-up, the pump should operate. If it does not
come on, check the circuit wiring for errors and ensure that it is powered up and the voltage is correct. Check the devices in the circuit
(pump, switching relay, etc.) for faults. If the pump operates properly when the circuit is powered up, disconnect the power and remove
the jumper. Repeat this step for the DHW pump / valve circuit.

Make sure power to the Boiler circuit is off and install a jumper in the terminal plug between the

Stage 1(11 and 12) terminals. When

the circuit is powered-up, the boiler should operate. If it does not come on, check the circuit wiring for errors and ensure that it is
powered up and the voltage is correct. Check the devices in the circuit (limits, flow switches, etc.) for faults. If the boiler operates
properly when the circuit is powered up, disconnect the power and remove the jumper. Repeat for Stage 2.

Caution

The tekmar Two Stage Boiler & DHW Control 252 is an operating control and is not certified or intended
for use as a safety device. Under no circumstances should safety limit devices be left disconnected
after installation of this control. The installer shall check all applicable code requirements and obtain
necessary inspections to ensure that the installation is in compliance with those requirements.

Terminal plug pushed into

its header on the control

Settings

15 16 17

20 21 22

10K

Sen

Com
Sen

Sup

Sen

DHW

Sen

UnO

Com
Sen

Out

Sen

RTU

Connect the control

Turn the power off and make sure all test jumpers have been removed from the
plugs.

Connect the plugs to the control by carefully aligning them with their respective headers
and pushing them upwards into the headers. The plugs should snap firmly into place.

The control is now ready for set-up and operation.

Heat Demand switch

When the heating system uses zone valve end switches or some other means of delivering an
external heat demand signal to terminals

Heat Dem — Heat Dem (1 and 2), set this selector switch

to "External (1 & 2)" and the control will be enabled when it receives a 24Vac signal from the heat
demand circuit.

If an external heat demand signal is not used, set the switch to "Permanent".

Stage 1 & 2 Auto or Off switch

When a Stage switch is set to "Auto", that stage becomes active and its boiler is available. If the
Stage switch is "Off", the control will ignore that stage and not turn it on.

Rotate switch

When set to "Rotate", the firing order of the boilers will change whenever one stage accumulates
48 hrs more running time than the other. When set to "Off", Stage 1 is always the lead boiler.

Auto

Stage

1 2

Perm. Heat Demand

External Heat Demand

Indoor sensor

Zone control

DHW during unoccupied
DHW priority

Rotate

Off

DHW valve

DHW pump