Scope
This document describes functions of controls on heaters with conventional control panels. It applies to both HC heaters (Fig. 1) and HCS heaters. (Note: conventional control panels have status lights as shown in Fig. 2.)
Figure 1. Heatec HCS heater with conventional control panel.
General
Key operator controls and status lights are on the main control panel (Fig. 2.). Controls on the front of these panels allow the operator to start and run the heater.
A variety of other controls related to safe operation are located at various places on the heater. These devices will shut down the heater when certain undesirable conditions are present. These devices control an electrical circuit known as a limit circuit. The limit circuit is the key to troubleshooting.
CONTROL PANEL
Controls on the outside of the control panel (Fig. 2) consist of status lights, switches, flame monitor, two controllers, an alarm horn and operating handle. Controls located inside the control panel include circuit breakers, auxiliary contacts, and relays. (See Figs. 3, 4 and 5.) Each of these items is discussed below. The words set in capital letters match the labels on the panel.
EMERGENCY STOP control (Fig. 2)
Push in this control to immediately shut down the heater. Use it only in an emergency. The control incorporates a light that comes on when the control is pushed in. Unlike using the HEATER CONTROL switch to shut down, the emergency stop control removes electrical power from all other controls and shuts down the heater without a post purge.
POWER ON indicator light (Fig. 2)
This indicator light denotes the status of power to the control panel. The light is on when 120 Vac, single phase, 60 hertz power from the Heatec control transformer is connected to the terminal bus within the panel. When there is no power connected to the terminal bus the light is off. The light usually has a white lens.
HEAT DEMAND indicator light (Fig. 2)
An indicator light that indicates the status of the burner control relay during normal operation. When the light is on the relay contacts are closed, which means that the relay is energized. When the light is off the relay contacts are open, which means that its coil is not energized. The coil is controlled by the Honeywell UDC3300 modulating controller and the HEATER CONTROL switch. The light has a blue lens. The light is on when the controller is calling for heat. It is off when the controller is not calling for heat.
LOW MEDIA LEVEL indicator light (Fig. 2)
An indicator light that denotes the level of thermal fluid in the expansion tank during normal operation. It is electrically connected to the low media level relay, which is controlled by a float switch mounted in the expansion tank (Fig. 8).
When the light is on, the level of fluid in the expansion tank is within normal operating range and the level switch and relay contacts are closed. When the light is out, the level of fluid in the expansion tank is abnormally low and the switch and relay contacts are open.
The float switch in the tank is also part of the limit circuit and will shut down the heater when opened. Moreover, when it opens it also disables the circulating pump circuit. The switch automatically closes when the fluid level in the tank is restored to normal.
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