LAARS Rheos RHCV - Install and Operating Manual - Manual (Page 25)

Rheos Boiler and Water Heater Page 25
sluggish with the control set to medium, the “Fast”
setting may be an improvement. The “Fast” setting
will only be used when the rate of change at the sensor
is very rapid. In most cases, this setting is too fast for
the Rheos.
5.6 External Control Connections
Rheos units are built with a selector switch and
a terminal strip to allow the Rheos to receive a 0-
10VDC signal from an external controller (such as a
building automation system or multiple boiler control).
When the selector switch is in the “Rheos
Control” position, the Rheos will be modulated by the
unit’s factory-mounted modulating control.
When the switch is in the “External Control”
position, the unit look for a 0-10VDC signal from an
external (field-supplied) controller.
To interlock the external boiler control with the
Rheos, the call for heat signal MUST be connected to
the field interlock terminal strip on the Rheos (shown
in Figure 18). Be sure to remove the factory-installed
jumper between the field interlock terminals. The
0-10VDC modulating signal MUST be connected to
external control terminal strip, located to the right
of, and behind the front panel. The terminal strip is
labeled “0-10VDC +” and 0-10VDC –” to indicate
which terminal received the hot signal (+) and which
terminal receives the common signal (-) from the
controller.
The Rheos unit will modulate between 4.7V and
10V (for 50% and 100%, respectively). Anything less
than 4.7 volts will result in 50% of full fire.
For the external control to modulate the Rheos,
the selector switch on the front panel must be in the
“External Control” position.
Important Note: DO NOT MAKE/BREAK RHEOS
LINE VOLTAGE TO SIGNAL CALL FOR HEAT. A“call
for heat / end call for heat” MUST be connected to the
field interlock terminals. The Rheos does not recognize
0 volts as a signal to shut off. If the call for heat is not
connected between the field interlock terminals, the
Rheos will remain in low fire when it sees 0 volts as a
modulating signal.
Caution
Rheos supply voltage must not be disengaged,
except for service or isolation, or unless otherwise
instructed by procedures outlined in this manual. To
signal a call for heat, use the 24V field-interlock, as
shown in the wiring diagram(s).
Some Rheos components are designed to have
constant voltage during normal operation. If Rheos
supply voltage is toggled as a call for heat signal,
premature failure of these components may result.
5.7 Wiring Diagrams
Caution
Label all wires prior to disconnection when servicing
controls. Wiring errors can cause improper and
dangerous operation. Verify proper operation after
servicing