Troubleshooting an Electric Baseboard Heater

Updated on December 19, 2017
Bert Holopaw profile image

Bert spent 25 years working as a home-improvement and residential construction contractor in central Florida.

Electric baseboard heaters provide instant heat.
Electric baseboard heaters provide instant heat. | Source

Homes without a centralized heating system often have electric baseboard heaters spread throughout the house. Even during normal operation, an electric baseboard heater takes a lot of abuse. Anything from carbon buildup between its thermostat's contacts to a loose electrical connection in the circuit-breaker panel can cause system failure. Troubleshooting the baseboard heater's electric circuit pinpoints the exact fault.

The baseboard heater's identification label, usually located on a label inside one of the electrical compartments, lists the heater's manufacturer, the model and serial numbers, and gives the individual heater's electrical requirements. Installers use this information to determine the correct wire and circuit breaker size. Replacement units should have compatible ratings.

Keeping a baseboard heater on a bare wall limits fire danger.
Keeping a baseboard heater on a bare wall limits fire danger.

How an Electric Baseboard Heater Works

Before a technician can troubleshoot an electric baseboard heater, he must understand it. The system starts inside the home's electric service panel with a circuit breaker. A set of wires run from the circuit breaker to either a wall-mounted or a built-in thermostat. When the thermostat detects a heating demand, its contacts close. This allows the electricity to pass on to the high-limit switch, mounted inside the baseboard heater's electrical-connection compartment. A high-limit switch protects the system from overheating. As long as the baseboard heater's temperature remains within tolerance, the high-limit switch remains closed, allowing continuity between the limit switch's wire terminals. Electric current then energizes the element, creating heat.

Most baseboard heaters operate on a dedicated 240-volt circuit and utilize a double-pole thermostat. A dedicated circuit powers one device. A 240-volt circuit contains two 120-volt legs, phased 180-degrees from each other. The actual voltage at the home depends on the electric company's output, transmission resistance and the home's distance from the electric plant. A double-pole thermostat has two sets of contact points; one set for each leg. A single pole thermostat has one set of contact points and a solid buss bar between the second leg's wire terminals. If a 240-volt baseboard heater uses a single-pole thermostat, the entire circuit remains live at all times.

A home's electric-service panel contains the baseboard heater's circuit breaker.
A home's electric-service panel contains the baseboard heater's circuit breaker.

The Baseboard Heater's Circuit Breaker Trips Instantly

When a circuit breaker trips instantly, part of the electric circuit contains a short. This type of issue usually leaves some sort of visual evidence, such as a burnt wire terminal. Turn the circuit breaker to the "Off" position; for safety's sake, never rely on the tripped position as a disconnect. Open up the baseboard heater's electrical compartments and inspect each part and its wire connections. Follow the wire between the electric-service panel and the thermostat, looking for any kind of damage. Pay special attention to the wire staples. The staples should hug the wire's sheathing, not crush it. A staple install too tightly can damage a wire strand's insulation, which leads to overheating.

Sometimes an electrical short develops inside a component and does not have visual evidence. Technicians find these shorts with a multimeter. Remove the wires from the thermostat's line leads. Turn a multimeter to its resistance mode. Check for continuity between the set of wires leading to the service panel. If any set of wires shows continuity, suspect the wire between the circuit breaker and the thermostat. If not, reconnect the thermostat's line leads.

Disconnect the baseboard-heater's thermostat load leads. Turn the thermostat to its hottest position. Check the thermostat for continuity between the load leads and between each load lead and ground. If the meter shows any continuity, replace the thermostat. Test the limit switches and elements, using the same method. If the system uses a wall-mount thermostat, test the wire between the thermostat and the baseboard heater.

Circuit breakers are brand and type specific.
Circuit breakers are brand and type specific. | Source

Baseboard Heaters that Work for a Short Period Before Tripping the Circuit Breaker

Was the malfunctioning baseboard heater or its circuit breaker recently replaced? If so, use the units' identification stickers to verify the new heater's element matches the old one. A larger heater often requires thicker gauge wire and a circuit breaker with a higher amperage. Generally, baseboard heaters up to 4000 watts use 12-gauge wire with a 20-amp circuit breaker and baseboard heaters over 4000 watts require 10-gauge wire and a 30-amp circuit breaker.

Does the circuit breaker feel hot? If so, calculate the circuit's total amperage load and verify the circuit breaker meets the minimal rating. The circuit breaker should exceed the load total by 125 percent. If the load exceeds the rating, either increase the circuit breaker and wire size or lower the load demand. Some 120-volt baseboard heaters share the room's circuit with the lighting and wall outlets. If so, add the outlet's typical power usage to the heater's load rating. A 240-volt system usually operates on its own circuit and does not have this issue. Check for a loose wire connection throughout the system. Let the circuit breaker cool down and reset the breaker's toggle switch. If the problem persists, replace the circuit breaker.

The Baseboard Heater Will Not Turn On

When an electric baseboard heater's thermostat turns on, the heater's circuit closes and its element energizes. A fault anywhere in the circuit opens the pathway, turning off the element. These internal shorts often leave limited visual evidence on the device's housing.

Open the home's electrical-service panel. Flip the appropriate circuit breaker to the "On" position. Turn a multimeter to the VAC position. If the system uses a double-throw circuit breaker, place a probe on each wire terminal. If the system uses a single-throw breaker, place one probe on the wire terminal and the other probe on the service panel's ground buss. Read the meter. A functioning single-throw circuit breaker should read about 120-VAC and a working double-throw breaker should transmit roughly 240-VAC. If the meter reads 0-VAC, replace the breaker. If a double-throw breaker reads about 120-VAC, replace the breaker.

Turn off the system's circuit breaker. Open the baseboard heater's thermostat compartment. Remove the thermostat. Turn the thermostat to its highest temperature setting. Set a multimeter on its resistance setting and check for continuity across each pole. If the thermostat fails to show continuity across either pole, replace it with an approved model. Hold the multimeter probes against one set of the baseboard-heater thermostat leads. Maintain contact while turning the thermostat to its lowest temperature setting. The thermostat should lose continuity when the thermostat no longer detects a need; the ambient temperature exceeds the thermostat's setting. Repeat this across the second pole, if applicable. Replace the thermostat if it fails any test.

Source

Remove the wire connectors from the thermal limit switch's two wire terminals. Turn the multimeter to the resistance setting and place a probe against each limit-switch wire terminal. The meter should show continuity. If not, replace the device. Under normal operating conditions, a thermal-limit switch remains in the closed position. Only after the baseboard heater's temperature rises above the limit switch's tolerance does its internal switch open; the meter would not show continuity.

Disconnect the leads from the element's terminals. Test the element for continuity, using the multimeter. The element should show continuity cross its terminals. If not, the element has failed. If the element has failed, consider replacing the entire unit. The low cost of a new unit usually does not exceed a replacement element's price by very much.

Electric Baseboard Heater That Does Not Turn Off

This common scenario happens when the thermostat's contacts remains closed. Eventually the limit switch will open and turn off the heater until the housing's temperature drops into tolerance. This turns the heater back on, possibly giving the impression that the thermostat functions randomly. A light tap on the thermostat may temporarily release the stuck internal part; however, this will not permanently fix the issue. Replace the thermostat with an applicable replacement part as soon as possible.

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© 2014 Bert Holopaw

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    • profile image

      merlin 4 months ago

      3 wires come through the wall a ground 2 wires with 120 volts each base board will not heat up . checked ohms on heater and it's around 30.5 . what am I not seeing ?

    • profile image

      Ross 5 months ago

      I have 220V power to both leads before and through the temp adjustment thermostat on the heater. the continuity is good through the element but heat is produced. What am I missing?

    • profile image

      Sam Bell @ sbell@juno.com 9 months ago

      Very good info

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