Lights Dim when Electric Water Heater Turns On? (Causes + What to Do)

Some or all of the lights in the house may dim when the heater is switched on.

While the heater may still be able to supply hot water, it may take longer to heat plus you may have concerns and some questions such as:

What causes the dimming? Is it normal? Should you do something about it?

This post explains the likely cause of the dimming of the lights and what you can do to stop it.

Quick Answer

Dimming of the lights is usually a result of the drop in available voltage at the lights which can be detected by a good quality meter. Read on to find out why this happens.

Reasons Why Lights Can Dim with Water heater On

If the lights dim, it may be because of the following:

Note: The suggestions below may involve working with electricity and can result in an electric shock, injury, or even death. Make sure you contact a qualified electrician.

#1. Loose wire connections at the water heater connection box, sub-panel, or main panel. Inspect the wire connections in the above mentioned places and confirm that they are securely fastened with no loose wire, or sparking connections that can lead to the dimming of the lights.

This will involve turning off the main breaker, checking and tightening any loose wire connection to the live, neutral, and ground bars in the main panel and or sub-panel.

#2. The electric circuit connections may be overloaded or undersized for the current draw by the water heater. Is the electric heater on a shared or dedicated circuit? The water heater should be connected to a dedicated circuit.

Consult the water heater manual for the recommended electric circuit amperage and make sure it is what the electric water heater is connected to.

#3. It could be a problem too with the supply voltage. Is the supply voltage low? Perhaps your house is at the end of the supply line.

Does the dimming happen at all times of the day or only during the night during peak hours?

Do other appliances with a large power draw such as an AC, or microwave cause the lights to dim?

If so, assuming they are on different electric circuits, it might be a supply issue in which case you’ll need to contact the power company.

Is this Normal? Problem with the Water Heater?

The lights shouldn’t be dimming. It is possible for a water heater to turn on without noticeable dimming of lights for as long as the heater is on. Check here for possible causes of dimming.

Why you Need to Fix the Lights

Dimming of lights should be investigated and rectified. Loose sparking connections or undersized wires can cause wires and or insulation to burn a potentially causing a fire, injury and damage to property.

Related Questions

Why do Lights get Brighter with Heater On?

If the lights get brighter when the heater is turned on, it is possible the there’s a loose neutral wire connection.

Contact a qualified electrician for assistance.

Closing Thoughts

If the lights in the house dim when the water heater is turned on, it may be because of a loose wire connection, an overloaded circuit, or even a problem with the supply from the power company.

Do not hesitate to contact a qualified electrician.

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