Frontier Oil Heat – PN 10-2021 – October 2021 - 27 -
Display Manager Return Sensor (Thermistor) Testing
The temperature sensor in the return line allows better boiler control, and virtually eliminates condensation caused by
cold returns.
The temperature sensor is a thermistor sealed with epoxy inside a stainless steel well. The thermistor communicates
continuously with the Manager thousands of times a minute.
The Display Manager is the tester of the display manager thermistor. It verifies that it is connected and working
properly, if not, will either say “Sensor Fault, Replace Soon”, indicating that one pair is bad or display the E100 or
E190 error code.
The thermistor can be tested with an ohm meter, at room temp (approx. 77F) it should read ~10K Ohms between
the black and red wires and between the white and red wires. As long as one pair is good, the manager will read
the correct return temperature but display the “Sensor Fault, Replace Soon” message.
Never connect 24 volts to the black, white or red sensor terminals (labeled B, S, or R.)
A caution: T4 thermostat input is adjacent to R, the red sensor terminal. When making thermostat connections,
never do so with power on.
Once firm proper connections have been made, power up.
WARNING: Do Not Jump!
To test the functioning of each output zone, never apply a jumper to the Energy Manager output terminals.
The easiest way to test each zone output is to remove the red sensor lead. The Manager should go into Service
Board Mode (E100) for 10 minutes, followed by Classic Manager Mode (E190). Adjust each thermostat to call for
heat and the corresponding zone should come on if working properly.
Rule #1: Never use a jumper to test the function of the Energy Manager.
Rule #2: Never use a jumper to test the function of the Return Sensor.
Rule #3: Never use a jumper to test the zones outputs.
Rule #4: Only use a jumper from A1 to the thermostat inputs, if you can’t reach the thermostats.
Rule #5: Always carry a Service Board with you.
Line Voltage Relays
Remember that behind the Manager is the junction box with the line voltage relays. The line voltage relays are
controlled by the Manager.
The burner and circulator power is controlled by one line voltage relay. If both burner and circulator are without power,
check the relay.
If the domestic hot water circulator does not have power, check the hot water relay.
If equipped with an inducer and the inducer does not have power, check the inducer relay. Also check to be sure dip
switch #2 is turned “on”.
Line Voltage
System 2000 requires 120 VAC. The supply voltage must be within 108 VAC min / 132 VAC max for reliable
operation of the boiler and the Manager. An easy way to check the supply voltage is to plug a volt meter in at the service
outlet located on the system junction box.
Surge Suppression
The Relay Board located in the system junction box is equipped with built-in surge suppression on the 120VAC circuit.
Older systems can be retrofitted using a plug-in surge suppressor.
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