How to Tell If Your Modem Is Bad
A bad modem usually shows itself through one of three patterns: your internet cuts out repeatedly even though your service is paid up, your speeds drop far below what you pay for and stay low, or your modem won't turn on or restart properly. The most common sign is the restart cycle—your modem loses connection, the lights flicker, it reboots on its own, and then connection returns for a few minutes before it happens again. This cycle can repeat every few minutes or every few hours.
Before you assume the modem itself is broken, you need to rule out the things that look identical but aren't: a loose cable, a problem with your internet service provider's network, or interference from other devices. A bad modem and a service outage feel the same to you, but they require completely different fixes. The steps below will help you tell them apart.
Key Takeaways
- Constant rebooting, no internet light, or speeds far below your plan speed are the clearest signs a modem is failing.
- Check your cables first—a loose connection to the wall outlet or to your router can mimic a bad modem.
- Call your internet provider to confirm their network is working in your area before you replace the modem.
- Modems typically last five to seven years; if yours is older and failing, replacement is usually cheaper than repair.
- A modem that overheats, smells like burning plastic, or has visible damage should not be used and needs when ready replacement.
The Restart Loop: Most Common Sign of a Failing Modem
If your modem restarts on its own every few minutes or every hour, and this happens even when you are not using the internet, the modem itself is almost certainly the problem. You will see the lights go dark, then come back on as it boots. During the restart, you lose internet completely for 30 seconds to two minutes.
This is different from a normal restart, which you do intentionally by unplugging the modem for 30 seconds. A modem that restarts without your input is usually overheating, has a failing power supply, or has internal memory that is corrupting. None of these can be fixed by you—the modem needs to be replaced.
Before you buy a new one, unplug the modem and leave it off for five minutes. Let it cool completely. Plug it back in and watch it for 24 hours. If it restarts again during that time, it is bad. If it stays stable, the restart may have been a one-time glitch caused by a power surge or a temporary network issue.
No Internet Light or Lights That Won't Turn On
Every modem has indicator lights on the front. The exact names vary by brand—some say "Internet," some say "Online," some say "WAN"—but there is always one light that shows whether the modem has a connection to your service provider's network. If that light is off or red when your internet is supposed to be working, the modem is not communicating with the network.
First, check that the cable running from the wall outlet to the modem is pushed in firmly on both ends. Coaxial cables (the thick ones with the metal twist-on ends) come loose easily, especially if someone bumped the modem or if pets are nearby. Unplug the modem, wait 10 seconds, and plug it back in. Watch the lights as it boots—they should go through a sequence of colors or blinks before settling into a steady state.
If the lights never turn on at all, even after a full restart, the power supply inside the modem may be dead. Try a different power outlet in a different room to rule out a tripped breaker or a bad outlet. If the modem still does not light up, it needs replacement.
Speeds Much Slower Than Your Plan Promises
If you pay for 100 Mbps but consistently see 20 Mbps or lower, and this has been happening for weeks, a failing modem is one possible cause. However, this is also the most common symptom to misdiagnose, because slow speeds can come from your service provider's network, from Wi-Fi interference if you are using wireless, or from too many devices using the internet at once.
Run a speed test on a device that is plugged directly into the modem with an ethernet cable, not through Wi-Fi. Go to speedtest.net or fast.com and run the test at different times of day—morning, afternoon, evening. Write down the results. If speeds are consistently 50% or lower than your plan, and you are using a wired connection, contact your internet provider and tell them your speeds. They can check their network from their end. Many providers will send a technician to test the line for free.
If the provider confirms their network is working correctly and your speeds are still low, the modem may be failing. Modems have internal processors that can degrade over time, causing them to handle data more slowly even though they are still technically working.
Modem Overheating or Physical Damage
A modem that is too hot to touch, that smells like burning plastic, or that has visible cracks or water damage should not be used. These are safety issues. Unplug it when ready and do not plug it back in.
Modems generate heat and need airflow around them. If yours is in a closed cabinet, inside a shelf with doors, or stacked under other equipment, it may overheat even if it is not broken. Move it to an open space where air can circulate on all sides. Leave at least two inches of space above and below it. If it still overheats after you have moved it, the internal cooling fan or the power supply is failing and the modem needs to be replaced.
Water damage is not always visible from the outside. If your modem got wet—from a spill, a leak, or humidity—it may work for a few days and then fail suddenly. If you know it has been exposed to water, replace it rather than waiting for it to fail.
How to Rule Out Your Internet Service Provider's Network
Before you buy a new modem, confirm that the problem is not on your service provider's side. Call their customer service number (it is on your bill) and tell them you are having connection issues or slow speeds. They will ask you to restart the modem while they listen, and they will check their network to see if there are outages in your area or problems with your account.
Ask them specifically: "Is there an outage affecting my address?" and "Are you seeing any errors on my line from your end?" Write down what they tell you. If they say the network is fine and the line looks good, the problem is your modem or your equipment. If they say there is an outage, ask when it is expected to be fixed and check back in a few hours.
Some providers will also tell you the signal strength they are seeing from your modem. If they say the signal is weak or unstable, it can mean either a bad modem or a loose cable. Ask them to walk you through checking all the cables before you assume the modem is bad.
When to Replace Versus When to Call a Professional
Modems are not repairable by consumers. There are no user-serviceable parts inside. If the modem is bad, it must be replaced. The only question is whether you buy a new one yourself or rent one from your service provider.
If your modem is rented from your internet provider, call them and tell them it is not working. They will send you a replacement at no charge and will provide a prepaid label to return the old one. This usually takes three to five business days.
If you own the modem, you will need to buy a new one. Check your service provider's website for a list of modems they support—not all modems work with all providers. Write down your service plan type (cable, fiber, DSL) and your plan speed, because these determine which modems are compatible. Most modems cost between $50 and $150. Avoid the cheapest options; a modem in the $80 to $120 range will last longer and handle higher speeds better.
Frequently Asked Questions
Can a modem be bad but still show an internet light?
Yes. A modem can have an internet connection but still be failing internally. If it is rebooting constantly, overheating, or delivering speeds far below your plan, the connection light being on does not mean the modem is healthy. The light only tells you whether the modem can see the network, not whether it is working properly.
How long do modems usually last?
Most modems last five to seven years before they start to fail. If yours is older than that and showing signs of trouble, replacement is almost always the right choice. Older modems also may not support newer, faster internet speeds even if they are technically still working.
What if I restart the modem and it works fine for a week, then fails again?
Intermittent failures that come and go are still failures. A modem that works sometimes and breaks sometimes is degrading. It will fail more often as time goes on. Plan to replace it within the next month rather than waiting for it to fail completely.
Can a bad modem damage my router or other equipment?
A failing modem will not damage your router or other devices. They are separate pieces of equipment. However, a modem that is overheating or has visible damage could pose a fire risk, so it should be unplugged and replaced when ready.
Do I need to do anything special when I get a new modem?
When you install a new modem, plug it in and let it boot for two to three minutes. The lights will go through a startup sequence. Once they settle into a steady state, your internet should work. You may need to restart your router and your devices, but the modem itself requires no setup. If your service provider sent the modem, they may have already activated it on their end.