Intertherm Electric Furnace Troubleshooting Guide

The Intertherm Electric Furnace Troubleshooting Guide provides clear, step-by-step solutions for common electrical furnace problems homeowners face, including no heat, short cycling, blown breakers, and noisy operation. This guide focuses on safety, diagnostic steps, and likely fixes to help users identify whether a simple repair, a thermostat adjustment, or a professional service call is needed.

Symptom	Likely Causes	Quick Fix
No Heat	Tripped breaker, faulty thermostat, open heating elements	Reset breaker, check thermostat, test elements
Short Cycling	Overheating, clogged filter, faulty limit switch	Replace filter, inspect limit switch, ensure airflow
Blown Breaker	Shorted element, loose wiring	Turn off power, inspect elements and wiring
Noise	Blower motor bearings, loose panels, arcing relays	Tighten panels, lubricate or replace motor, check relays

How Intertherm Electric Furnaces Work

An Intertherm electric furnace uses electrical resistance heating elements and a blower to distribute warm air through ductwork. A thermostat signals the control board to energize contactors that supply line voltage to the heating elements. Safety devices such as limit switches and fuses protect against overheating and electrical faults.

Understanding the basic components—thermostat, contactor/relays, heating elements, blower motor, limit switches, and the control board—helps diagnose issues more efficiently and safely.

Safety First: Before Troubleshooting

Always turn off power at the service disconnect or breaker before opening the furnace access panels. Electric furnaces operate at high voltages that can cause serious injury or death. Use a non-contact voltage tester to confirm power is off and wear insulated tools and gloves when handling wiring.

Document model and serial numbers from the furnace data plate before ordering parts or calling support. Keep manufacturer manuals and wiring diagrams handy for reference.

Tools And Materials Needed

• Multimeter (AC/DC voltage and continuity)
• Non-contact voltage tester
• Screwdrivers and nut drivers
• Needle-nose pliers and wire strippers
• Replacement fuses, contactors, heating elements, filters
• Manufacturer wiring diagram and parts list

Common Symptoms And Step-By-Step Troubleshooting

No Heat But Blower Runs

If the blower runs but no heat is produced, primary suspects are the thermostat, contactor/relay, heating elements, or safety fuses. This symptom indicates the fan receives power but heating circuits do not.

1. Verify Thermostat Settings: Ensure thermostat is set to HEAT and temperature setpoint exceeds room temperature. Check battery power if applicable.
2. Check Breaker And Disconnect: Confirm the furnace breaker and external disconnect are ON. Reset if tripped.
3. Inspect Contactor/Relay: With power on and call for heat, listen for a click. If no click, measure 24VAC to the contactor coil or control voltage. Replace contactor if coil receives correct control voltage but contacts do not close.
4. Test Heating Elements: With power off, use a multimeter to check continuity of each element. An open element indicates replacement is needed.
5. Check High-Limit/Fuse: Measure continuity on high-limit switches and any inline fuses. Replace any open safety devices after addressing cause of overheat.

Furnace Doesn’t Turn On At All

A completely dead furnace points to power supply issues: tripped breakers, blown fuses, failed service switches, or internal control board failure.

1. Confirm Home Power: Verify other circuits work. Reset the specific furnace breaker.
2. Inspect Service Disconnect: Make sure the external safety switch near the unit is engaged.
3. Check Line Voltage: With care, measure incoming line voltage at the furnace terminal block. No voltage suggests electrical panel or wiring issue—contact an electrician.
4. Examine Control Board: Some Intertherm models have low-voltage LEDs on the control board. No LED when power is supplied may indicate board failure.

Furnace Short Cycles Or Runs Too Frequently

Short cycling reduces comfort, increases wear, and can cause overheating. Common causes include dirty filters, blocked return vents, oversized furnace, or a failing limit switch.

1. Replace Air Filter: A clogged filter restricts airflow and can trigger the high-limit switch.
2. Check Airflow And Vents: Ensure returns are unobstructed and supply registers are open.
3. Inspect High-Limit Switch: A faulty limit may cut heat prematurely. Test for continuity and replace if intermittent.
4. Assess Thermostat Placement: Thermostats near heat sources or in direct sunlight can cause short cycles; relocate if necessary.

Breaker Trips Or Blown Fuses On Heat Call

Repeated breaker trips usually indicate a short circuit or overloaded circuit. Heating elements can short to ground or wiring may be loose, creating arcing.

1. Turn Off Power: Open panels and visually inspect for burnt wires or melted insulation.
2. Test Elements For Short To Ground: Use an ohmmeter between each element terminal and ground. Low resistance to ground means replacement.
3. Tighten Terminal Connections: Loose line connections increase resistance and heat, potentially tripping breakers.
4. Check Breaker Size: Ensure the breaker matches furnace specifications. Never use an oversized breaker to hide wiring faults.

Noisy Operation: Buzzing, Clicking, Or Rattling

Operational noises often stem from failing blower motors, loose panels, failing relays, or expansion noise from rapid heating.

1. Secure Panels: Tighten all access panel screws and check duct screws.
2. Listen For Relay Arc: Repeated buzzing when elements energize may indicate a failing contactor; replace if noisy.
3. Inspect Blower Motor And Wheel: Worn bearings produce humming or screeching. Replace motor or lubricate if serviceable.
4. Check For Loose Ductwork: Vibration can transmit through ducts causing rattles; fasten or add isolation straps.

Testing And Replacing Heating Elements

Heating elements are typical failure points in electric furnaces. They are tubular and can burn out or short. Testing requires power off and multimeter continuity checks between element terminals.

Replace elements with manufacturer-specified parts. When replacing, inspect element mounts and terminal blocks for corrosion or heat damage and replace related hardware as needed.

Thermostat And Control Issues

Thermostats send the 24VAC signal to start heating. A faulty thermostat, incorrect wiring, or a weak transformer can stop the furnace from running. Test by jumping R to W at the furnace control to simulate a call for heat.

If jumping R to W starts the furnace, the thermostat or its wiring is the issue. Check thermostat batteries, wiring terminals, and settings before replacing the thermostat.

When To Call A Professional

Some conditions require licensed technicians: repeated breaker trips after repairs, suspected element short to ground, control board faults, damaged high-voltage wiring, and failed limit switches. Electric furnaces operate at lethal voltages; professional service ensures safety and correct repair.

Documentation of attempted diagnostics, model numbers, and error codes speeds technician response and avoids unnecessary service charges.

Maintenance Tips To Prevent Problems

• Change Filters Regularly: Every 1–3 months depending on usage and filter rating.
• Keep Vents Clear: Maintain at least 2 inches clearance around return grills.
• Annual Professional Inspection: Have a qualified HVAC technician inspect heating elements, wiring, and safety devices before cold season.
• Observe Operation: Note unusual odors, sounds, or cycling patterns and address them early.

Replacement Parts And Compatibility

Use Intertherm OEM parts or approved equivalents to maintain safety certifications and proper operation. Common replacement parts include heating elements, contactors, limit switches, blower motors, and control boards.

Cross-reference part numbers from the furnace data plate with manufacturer catalogs. Installing incorrect resistance elements or mismatched contactors can lead to poor performance or hazards.

Warranty And Manufacturer Resources

Check the furnace warranty before performing repairs. Many Intertherm units have limited warranties on components; unauthorized repairs may void coverage. Register the product when new and retain receipts for claims.

Manufacturer manuals, wiring diagrams, and tech bulletins are valuable resources. Intertherm (or parent company documentation) can provide diagnostic codes, wiring diagrams, and authorized service center lists.

Frequently Asked Questions

Can a homeowner safely replace heating elements?

Homeowners with electrical knowledge may replace elements with power off and proper tools, but should only proceed if comfortable with high-voltage wiring. When in doubt, hire a licensed technician to avoid injury and code violations.

What causes a furnace to smell when first turned on?

Burning dust after the first seasonal startup is normal; persistent burning smells suggest electrical arcing or insulation burning and requires immediate inspection.

How long do Intertherm electric furnaces typically last?

With proper maintenance, electric furnaces can last 15–20 years. Regular filter changes, annual inspections, and timely part replacements extend service life.

Quick Diagnostic Checklist

• Verify power to the unit and reset breakers.
• Check thermostat settings and batteries.
• Inspect and replace filters if dirty.
• Listen for contactor click and check 24VAC control signal.
• Test heating elements for continuity and shorts to ground.
• Inspect high-limit switches and inline fuses for continuity.
• Look for loose or burnt wiring and secure all connections.

Resources And Further Reading

Consult the Intertherm owner’s manual and wiring diagram for model-specific guidance. Trusted resources include the Air Conditioning, Heating, & Refrigeration Institute (AHRI) and the U.S. Department of Energy for energy-efficiency tips.

For electrical concerns beyond basic diagnostics, contact a licensed HVAC electrician or an authorized Intertherm service provider to ensure safe and code-compliant repairs.

Key Takeaway: Systematic, safe diagnostics—checking power, thermostat signals, contactors, and heating elements—resolve most Intertherm electric furnace issues; call a professional for wiring faults, repeated breaker trips, or control board failures.