Intertherm Furnace Troubleshooting

Looking at the troubleshooting manual of Intertherm furnaces given here you can easily fight the problems with repair if you face some. It gives the full description of the issues possible. In most cases it will help you to manage even the most difficult situation. Only if it doesn’t, it’s time to come for service on the issue taken place. So, the conclusion is as follows: don’t panic and read the guide.

Intertherm M1B Series Furnace Troubleshooting

Green LED Red LED Yellow LED Diagnostic Description
Off Off Control Fault (No Power)
Flash Flash L1/Neutral Polarity Fault
On On Normal Operation
On Flash Pressure Switch Closed Fault
Flash On Pressure Switch Open Fault
Flash Off Open Limit Switch Fault
Continuous Flash Low Flame Sensor Signal
On Flame Present

Intertherm M1M Series Furnace Troubleshooting

LED INDICATOR COLOR Flashing type Cause
Green led indicator Continuously On Restricted (hard) lockout
Flashing Soft lockout
Flashing-1/2 sec. on, 1/2 sec. off Lockout / Restricted Lockout
Flashing – 2 sec. on, 2 sec. off Recycle
Red led indicator Continuously On Cad cell is sensing flame – (could be flame or stray light)
Flashing Recycle
Yellow led indicator Continuously On Pump prime mode or reset button currently held for 15+ sec.
Flashing N/A

Intertherm M4RC Furnace Troubleshooting

Problem Solution
Burner Motor won’t Run – T-stat Calls for Heat 1. 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 Flame 1. 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 Up 1. 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 Up 1. 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 flash The control is in lock-out because the inducer centrifugal switch is or was stuck closed.
Two flashes The control is in lockout because the signal was not received by the control that the inducer centrifugal switch had closed within the time.
Three flashes The 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 flashes The control is in lockout due to a failure within the control board

Intertherm M7RL Series Furnace Troubleshooting

Steady ON Control OK
Steady OFF No power
Rapid flash False flame or internal control fault
One flash Limit switch is open
Two flashes Pressure switch is open
Three flashes Pressure switch is stuck closed
Four flashes Lockout due to failed ignition
Five flashes L1 neutral reversed or L1 voltage not present on L1