Wi-Fi Drops When the Aircon or Water Pump Starts

This complaint has a distinctive, easily recognised shape: the internet is fine all day, then drops exactly when the air conditioner starts, the water pump runs, or the washing machine hits its spin cycle. A few seconds later everything is normal again. Because what disappears is internet, people assume the problem is Wi-Fi. It almost never is.

How to confirm it, and how the two causes differ

Next time it happens, look at the router, not your phone. There are two possibilities, and they need different fixes:

• All the router lights go out and come back in sequence, as when first plugged in. That's an electrical problem, which is what this guide covers. What each light means is in the router indicator lights guide.
• The lights stay on, but the connection slows or stutters while the appliance runs. That's interference, not power. Skip to the last section.

If you can't catch it in the act, open the router's admin page and look for uptime. A number that's always small, hours rather than days, confirms the router really is rebooting repeatedly. Other causes of restarts are covered in routers that keep restarting.

Why the router gives up first

Electric motors, and that covers aircon compressors, water pumps, and washing machines, draw several times their running current at the instant they start. That surge makes the voltage across the whole house sag briefly, sometimes only a fraction of a second, often not long enough to dim the lights.

A router runs on a small adapter with almost no energy reserve inside. Half a second of low voltage is enough to make it die and start from scratch, including the one to two minute reconnection to the provider. TVs and fridges have components that ride through far longer dips, so they're unaffected. That's why the router is often the only device that appears broken, and why people wrongly conclude the router itself is faulty.

Three fixes, in order

1. A small UPS for the router and ONT

This is the actual solution, and cheaper than electrical work. A UPS supplies from battery when voltage sags, so a split-second dip never reaches the router. A UPS for a router doesn't need to be big; even the smallest handles both dips and a ten to thirty minute outage.

What gets missed: the ONT or modem must go on the UPS too. A router that stays up while the ONT dies still means no internet. If there's a switch, include that as well. Guidance in a UPS for your router, and the power figures in electricity cost of network equipment.

Note: a stabiliser is not a substitute here. It evens out voltage that's too high or too low, but still passes through an interruption. What's needed is reserve, not regulation.

2. Move it to a different circuit

If a UPS isn't possible yet, separate the circuits. A router sharing a socket, or a single breaker, with the water pump takes the hardest hit. Move the router to a socket in another room on a different circuit. This reduces the problem, though it rarely removes it entirely.

While you're at it, check the adapter. An ageing adapter produces unstable voltage and makes the router far quicker to give up on small disturbances. How to test it is in faulty router power adapter and replacement.

3. If the lights dim too, call an electrician

There's a limit worth admitting. If the house lights visibly dim every time the pump starts, or the breaker occasionally trips, the problem is no longer the network equipment but the electrical installation: insufficient contracted capacity, undersized cable for the load, or a loose connection. A UPS will hide the symptom at the router, but the cause remains and is a risk to the whole house. That part belongs to an electrician, not to a router admin page.

If the router lights never go out: interference

If the router doesn't reboot but the connection still degrades while the appliance runs, the cause is electromagnetic interference. Electric motors, especially older or unshielded ones, emit noise that disturbs the 2.4 GHz band. What usually fixes it:

• Move devices to 5 GHz, far less affected by motor noise. If the router uses one name for both bands, see what band steering is.
• Move the router away from the appliance, including from the cable running to it. Guidance in router placement.
• Change channel if a scan shows the current one is genuinely poor; see choosing the right Wi-Fi channel.

A fuller explanation of household interference sources is in Wi-Fi interference from other devices.

For businesses, this isn't about comfort

In a food stall, workshop, or clinic, a router that reboots when the compressor cycles means a QRIS transaction failing mid-payment and a customer waiting. A UPS for the router, ONT, and till is basic equipment, not an extra. See Wi-Fi for workshops and car washes, the harshest environment of them all.

The short version

Router lights going out means power, not Wi-Fi. Fit a UPS covering both router and ONT, move to a different circuit, and check the adapter. If the house lights dim too, that's an electrical installation matter. If the router never dies but the connection degrades while the appliance runs, that's interference, and the answer is 5 GHz.

Frequently asked questions