LAARS NeoTherm NTV (Sizes 399-850 MBTU/h) - Service Manual - Manual (Page 62)

52
Service Manual - NeoTherm 500
Servicing the Transformer
Fig. B34-1 - Transformer installation (typical)
The transformer changes the 120V AC input power
into 24V AC for use by the controls in the NT unit.
The transformer includes an integral 4 Amp circuit
breaker, and is mounted on the machine frame, near
the top of the unit. A reset switch on the bottom of
the unit can be used to reset the circuit breaker.
The transformer is sized for the appliance load only,
and should not be used to supply power to additional
field devices. Additional loads may cause the circuit
breaker to trip.
Yes
Unit starts
running?
Reconnect the sensor lead
Is Outdoor Reset enabled on the controller?
Check programming -
Example - Low boiler temp. set to 130°, heat setpoint set to 120°, so unit never fires.
Example - High and low boiler temps. set the same, so unit never fires.
The high temp. setting must always be higher than the low temp. setting.
Disconnect one lead from
outdoor temperature sensor
Note -
On units with the current interface produced before October 2012 -
If the sensor for outdoor reset is disconnected, the unit will operate at the highest setpoint,
as if the outdoor reset function was inoperative.
On units with the current interface produced after October 2012 -
The unit will operate at 140°F.
B33
Troubleshooting the Outdoor Reset System
B34