LOW FUEL PILOT PRESS. indicator light (Fig. 2)
An indicator light that denotes the status of the low fuel pilot gas pressure switch. When the light is on the fuel pilot gas pressure is normal and the switch is closed. When the light is out the fuel pilot gas pressure is too low and the switch is open. This switch is part of the limit circuit and will shut down the burner when open. The switch has a manual reset button.

Note: Not all heaters have a low fuel pilot pressure switch. But the panel may still have an indicator light for the switch. In that case the switch is replaced by a jumper wire. Thus, the light will react the same as it would with a switch in its normal pressure state.

HIGH FUEL GAS PRESS. indicator light (Fig. 2)
An indicator light that denotes the status of the high fuel gas pressure switch (Fig. 9) when the FUEL SELECTOR switch is set to GAS. When the light is on the fuel gas pressure is normal and the switch is closed. When the light is out the fuel gas pressure is too high and the switch is open. This switch is part of the limit circuit and will shut down the burner when open. The switch has a manual reset button.

Note: Not all heaters have a high fuel gas pressure switch. But the panel may still have an indicator light for the switch. In that case the switch is replaced by a jumper wire. Thus, the light will react the same as it would with a switch in its normal pressure state.

LOW FUEL GAS PRESS. indicator light (Fig. 2)
An indicator light that denotes the status of the low fuel gas pressure switch (Fig. 10) when the FUEL SELECTOR switch is set to GAS. When the light is on the fuel gas pressure is normal and the switch is closed. When the light is out the fuel gas pressure is too low and the switch is open. This switch is part of the limit circuit and will shut down the burner when open. The switch has a manual reset button.

Note: Not all heaters have a low fuel gas pressure switch. But the panel may still have an indicator light for the switch. In that case the switch is replaced by a jumper wire. Thus, the light will react the same as it would with a switch in its normal pressure state.

HEATER FUEL OIL PUMP AUX. CONTACTS indicator light (Fig. 2)
An indicator light that denotes the status of a set of auxiliary contacts on the motor controller that connects electrical power to the motor of the fuel pump. When the indicator light is on electrical power is connected to the pump motor. When the light is off the contacts are open because electrical power is not connected to the motor. The contacts are also part of the limit circuit and will shut down the heater when opened. The contacts automatically close when power is restored to the motor.

Note: only heaters with an external fuel pump have auxiliary contacts for the fuel pump. But the panel may still have an indicator light for the contacts. In that case the contacts are replaced by a jumper wire. Thus, the light will react the same as auxiliary contacts that are closed.

LOW FUEL OIL PRESS. indicator light (Fig. 2)
An indicator light that denotes the status of the low fuel oil pressure switch when the FUEL SELECTOR switch is set to OIL. When the light is on the fuel oil pressure is normal and the switch is closed. When the light is out the fuel oil pressure is too low and the switch is open. This switch is part of the limit circuit and will shut down the burner when open.

Note: Only heaters with an external fuel pump have a low fuel oil pressure switch. But the panel may still have an indicator light for the switch. In that case the switch is replaced by a jumper wire. Thus, the light will react the same as it would with a switch in its normal pressure state.

HIGH MEDIA TEMP. indicator light (Fig. 2)
An indicator light that denotes temperature status of the thermal fluid. It is electrically connected to contacts of the high media temperature relay (Fig. 5), which is controlled by the high media temperature controller UDC2300.

When the light is on, temperature of the thermal fluid is within normal operating range. When the light is out, the temperature of the fluid has exceeded the preset limit of the controller. The relay contacts are also part of the limit circuit, which shuts down the burner when the contacts are opened. The controller must be reset after the thermal fluid has cooled down to within the operating range.

HIGH FLUE GAS STACK TEMP. indicator light (Fig. 2)
An indicator light that denotes temperature status of gas in the exhaust stack. It is electrically connected to the high flue gas stack temperature switch ( Fig. 11) mounted in the exhaust stack. The manufacturer of this switch calls it a differential expansion temperature control.

When the light is on, temperature of the gas is within normal operating range and the switch contacts are closed. When the light is out, gas temperature has exceeded its factory setting of 1000 degrees F and the contacts are open.

The switch is also part of the limit circuit and will shut down the heater when the switch is opened. The switch must be manually reset, which requires removing its cover and pressing a reset button.

CIRC. PUMP AUX. CONTACTS indicator light (Fig. 2)
An indicator light that denotes the status of a set of auxiliary contacts (Fig. 4) on the motor controller that connects electrical power to the motor of the fluid circulating pump. When the indicator light is on electrical power is connected to the pump motor. When the light is off the contacts are open because electrical power is not connected to the motor. The contacts are also part of the limit circuit and will shut down the heater when opened. The contacts automatically close when power is restored to the motor.