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Section E: External Direct Drive Operation
When mode 7 is selected, the control allows for an external control to operate the boiler through an analog direct drive input
signal provided by a boiler sequencing control such as a tekmar Boiler Control 265. When in mode 7, the external heat demand
(CD and Ht D) and the DHW demand (CD and DHW D are disabled.
DIRECT DRIVE INPUT SIGNAL
An external boiler sequencer provides a positive 0-10 V (dc) input signal to the control +V(in) input (pin 10). The negative V
(dc) signal is applied to the Com/- input. The boiler burner remains off while the direct drive input signal range is between 0 to
0.5 V (dc). The Stage 1 contact remains on as long as the direct drive input signal is over 0.5 V (dc).
PUMP OPERATION
The pump contact close as soon as the direct drive input signal reaches 0.5 V (dc). Once the direct drive input
signal falls below 0.5 V (dc), the pump continues to operate until the Pump DLY purge expires, then the pump shuts off.
BOILER MAXIMUM TEMPERATURE
The external boiler sequencer is able to operate the boiler temperature. However, the BOIL MAX setting limits the highest
temperature at the boiler outlet sensor. Should the boiler outlet temperature exceed the BOIL MAX setting, the Stage contact
is opened to shut off the burner. The burner remains off for the minimum off time and the boiler outlet temperature falls 2°F
(1°C) below the BOIL MAX setting.
Section F: Domestic Hot Water Operation
When modes 1, 2, 3, 4, 5, or 6 are selected, the control is able to override the heat demand operation and respond to heat an
indirect domestic hot water (DHW) tank.
DHW DEMAND (Dem 2)
A DHW demand is required whenever the indirect DHW tank requires heating. A DHW demand is generated when a voltage
between 24 and 120 V (ac) is applied across the CD (common demand) and the DHW D (DHW demand). Once
voltage is applied, the control turns on the Dem 2 segment in the display. The control closes the DHW pump contacts, which
starts the DHW pump and the control turns on the DHW pump segment in the display.
BOILER TARGET DURING DHW OPERATION
The boiler target temperature is at least as hot as the DHW BOIL TARGET setting. If a heat demand is present during a DHW
demand, the boiler target is the higher of the two temperatures.
DHW OPERATION WITH PRIMARY / SECONDARY PIPING
When the boiler is piped in primary / secondary to the boiler and MODE
is set to 2, 4, or 6, the control operates the boiler pump together with the
DHW pump.
Ω
Model SF-10 Control Instructions Manual
Boiler
Supply
Sensor
11
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