Intertherm Furnace Troubleshooting

Intertherm M1B Series Furnace Troubleshooting

Green LEDRed LEDYellow LEDDiagnostic Description
OffOffControl Fault (No Power)
FlashFlashL1/Neutral Polarity Fault
OnOnNormal Operation
OnFlashPressure Switch Closed Fault
FlashOnPressure Switch Open Fault
FlashOffOpen Limit Switch Fault
Continuous FlashLow Flame Sensor Signal
OnFlame Present

Intertherm M1M Series Furnace Troubleshooting

LED INDICATOR COLORFlashing type Cause
Green led indicatorContinuously OnRestricted (hard) lockout
FlashingSoft lockout
Flashing-1/2 sec. on, 1/2 sec. offLockout / Restricted Lockout
Flashing - 2 sec. on, 2 sec. offRecycle
Red led indicatorContinuously OnCad cell is sensing flame - (could be flame or stray light)
Yellow led indicatorContinuously OnPump prime mode or reset button currently held for 15+ sec.

Intertherm M4RC Furnace Troubleshooting

Problem Solution
Burner Motor won’t Run - T-stat Calls for Heat1. Check the electrical supply to the furnace.
2. Verify the furnace furnace On-Off switch is in the ON position.
3. Defective thermostat circuit - white and red thermostat low voltage leads (M1/M5M, M1/M5B models). If the burner motor or combustion fan runs, check:
• Thermostat connections
• Thermostat
4. No voltage to control module - determine if 24 volts (or 120 volts) is available to the control module. If voltage is not available check for:
• Blown fuse, defective transformer, circuit breaker, no electrical supply.
• Limit switch open.
• Loose connections
Combustion Blower Runs - No Flame1. Defective centrifugal switch (M1B Model).
• Check the operation of centrifugal switch by removing end bell of the burner motor.
• Clean contacts of motor.
• Ifthe contacts are closed, replace the motor.
2. Defective pressure switch (M1M - 077 & 090 Models) - check air tube and electrical connections.
3. Burner in purge mode - allow 75 seconds for flame establishing period.
4. Check for proper electrical connections at purge timer, control box, or gas valve.
5. Check for gas supply - gas line valve on, control lever on
120 VAC Is Available At AMP Plua - lanitor Does Not Heat Up1. Disconnect power to the furnace.
2. Disconnect AMP plug to the ignitor, and check ignitor resistance with an ohm meter. Set on RX1 scale.
• Normal reading should be 40 - 75 ohms.
• If above or below this rating at room temperature change ignitor.
3. Check for continuity from ignitor receptacle to burner
Control Module is Powered - lanitor won’t Heat Up1. Disconnect ignitor leads at AMP receptacle and check for 120 volts at the plug during ignition sequence.
2. Replace ignition control if 120 volts is not available at AMP plug during ignition sequence.
Main Flame Ionites - Burner Locks Out• Ignition control is not properly grounded.
• Defective ignition control.
• Improper polarity of 120 volt power supply.
• Ignitor has hairline crack.
• Improper gas pressure or burner air adjustment is not allowing flame to contact ignitor tip for flame rectification.
• Misaligned ignitor does not allow flame to contact ignitor tip for flame rectification
Burner Short Cvclino - Thermostat Calls for Heat. Limit Switches Closed• Check for polarity.
• Check ground.
• Check flue.
• Check combustion air.
• Check gas pressure.
• Check orifice.
• Check the position of ignitor, a normal reading should be 40-75 ohms
24 Volts Supplied To Gas Valve Durina lanition - No Main Gas Flow• Gas valve may be defective. Replace if necessary.
• Gas piping may be plugged. Check for adequate gas supply to gas valve at union
Burner Operates - Insufficient Heat• Check thermostat for proper setting and location. Thermostat should not be located where it will be affected by another heat source.
• Check for clean filter and proper air flow.
• Check burner for proper gas firing rate.
• Be sure unit is not undersized for its thermal load.
• Check thermostat anticipator. The nominal setting is 0.4.
Circulation Air Blower Will Not Operate Even Thouoh The Burner Does Operate• Check thermostat G connection.
• Check wiring to motor.
• Check for a defective motor
Burner Flame Without Motor Runnina• Gas valve stuck open, check gas valve for proper operation (replace if necessary) and inspect heat exchanger.
• Check for 115 volts to the combustion blower motor; replace if necessary.
• If no power to combustion blower then check wiring and control module; replace if necessary.

Intertherm M5S Series Furnace Troubleshooting

One flashThe control is in lock-out because the inducer centrifugal switch is or was stuck closed.
Two flashesThe control is in lockout because the signal was not received by the control that the inducer centrifugal switch had closed within the time.
Three flashesThe control is in lockout because a failed ignition attempt, a gas valve error, or a false flame sensed during the warm up period. If false flame has been sensed, the control will return to normal operation, and repeat ignition sequence when the false flame is not present.
Four flashesThe control is in lockout due to a failure within the control board

Intertherm M7RL Series Furnace Troubleshooting

Steady ONControl OK
Steady OFFNo power
Rapid flashFalse flame or internal control fault
One flashLimit switch is open
Two flashesPressure switch is open
Three flashesPressure switch is stuck closed
Four flashesLockout due to failed ignition
Five flashesL1 neutral reversed or L1 voltage not present on L1