Combustion air auxiliary contacts
The auxiliary contacts are located inside the control panel. This is a set of auxiliary contacts on the motor starter (Fig. 4) that connects electrical power to the burner fan motor. The auxiliary contacts open a limit circuit if the circuit breaker for the burner fan motor is tripped. When the limit circuit opens it shuts down the burner in a lockout state. The display of the Fireye flame monitor (Fig. 2) will indicate LOCKOUT 3-P INTLK OPEN.

Figure 4. Auxiliary contacts for combustion
air and circulating pump motor controllers.

The burner cannot be restarted until the flame monitor and the burner circuit breaker is manually reset. The auxiliary contacts automatically close when power is restored to the motor.

Circulating pump auxiliary contacts
The circulating pump has a set of auxiliary contacts located inside the control panel (Fig. 4). The contacts are on the motor starter that connects electrical power to the motor of the fluid circulating pump. The auxiliary contacts open a limit circuit if the circuit breaker for the circulating pump motor is tripped.

The contacts are part of a limit circuit and shut down the heater when opened. The heater cannot be restarted until the flame monitor and the circulating pump circuit breaker is manually reset. The auxiliary contacts automatically close when power is restored to the motor.

High media temperature relay
This relay is located inside the control panel. It is a relay (Fig. 5) that opens a limit circuit if temperature of the media (thermal fluid) exceeds the preset limit of high media temperature controller (Fig. 2), which controls the relay. When the limit circuit opens, it shuts down the burner. The controller must be reset after the thermal fluid has cooled down to within the operating range.

Figure 5. Relays: HMT1, BC 1, LML 1.

 

OTHER CONTROLS

Thermocouples
Heaters without manifolds have one duplex thermocouple installed near the outlet of the helical coil. The thermocouple has two pairs of leads. One pair is connected to the UDC3300 controller for temperature regulation. The other is connected to the UDC2300 controller, which prevents temperature of the thermal fluid from exceeding its limits.

On heaters with manifolds, (Fig. 6) two duplex thermocouples are installed. Only one pair of leads from each thermocouple is used, leaving a spare set of leads.

One of the two thermocouple is installed near the outlet of the helical coil and is connected to the UDC2300 controller which prevents the temperature of the thermal fluid from exceeding its limits.

The other is installed in the manifold and is connected to the UDC3300 controller for temperature regulation. Note: fluid temperature at the thermocouple in the manifold could be as much as 50 degrees (or more) lower than its temperature at the thermocouple in the outlet.

Figure 6. Thermocouples in manifold and outlet of HC heater.