Written 6 Sep 2026. This is a how-to, not a product card.

When the house Wi-Fi password changed

You (or the ISP) changed the Wi-Fi passphrase. The old PC on radio is offline — SSH hangs, ads are back. Update the saved password on the computer. Skip a new mesh kit tonight.

Never joined house Wi-Fi yet? Start with put the old PC on house Wi-Fi. Radio joins, then flaps for no password reason? That is when house Wi-Fi on the old PC keeps dropping. Tech left a whole new gateway? Walk when the ISP swaps your router. This note is the narrow case: phones and laptops already use the new passphrase, but the old PC still has the old one saved.

Skip until the radio is how it reaches the house

If the computer is on a cable and SSH already works, you don't need this page. Prefer the cable when you can: a cable beats Wi-Fi for the computer. If the ISP swapped the whole router (new Wi-Fi name, new admin, new LAN), start with the ISP-swap walk instead. You need a keyboard and a screen on the old PC — SSH from the couch will fail until the radio joins again.

What this is

The computer stores the house Wi-Fi name and passphrase so it can join after every reboot. When you change that passphrase on the router (or the ISP does), phones get a prompt. The old PC does not. It keeps trying the old string, never gets a house number, and Pi-hole goes dark for the rest of the house. You sit at the computer, put the new passphrase in the same place the first join used, then confirm a house address. You don't buy a mesh kit for a wrong password.

Step 1: confirm it is the passphrase, not a dead box

On your phone, open the house Wi-Fi settings. Confirm the name (SSID) is the same one the computer used, and that you know the new passphrase. Other phones and laptops should already be online with that new string.

At the old PC: fans spin, screen wakes, keyboard responds. If it looks dead, fix power first: is it still on? or when the old PC won't boot. Lid sleep on a laptop: don't let the old laptop sleep.

From the keyboard:

ip -br addr

Look for a wlan or wlp line. No house number (no 192.168.… / 10.… on that line) while other devices are fine on the new passphrase is the classic wrong-password case. If the radio has a number and SSH still fails, this is not the password note — try when SSH won't connect.

Step 2: NetworkManager path (nmtui / nmcli)

Ask whether the menu tool is there:

command -v nmtui

If it prints a path:

sudo nmtui

Pick Edit a connection (or Activate, then edit). Open the house Wi-Fi row. Put the new passphrase in the password field. Save. Activate that connection. Skip to Step 4.

Or one line with nmcli (swap HouseSSID and the new passphrase — the string below is fake):

sudo nmcli connection modify "HouseSSID" wifi-sec.psk "example-new-pass"

sudo nmcli connection up "HouseSSID"

List saved Wi-Fi names if you are unsure of the connection title:

nmcli -t -f NAME,TYPE connection show | grep wireless

Step 3: Ubuntu Server netplan path (no nmtui)

If command -v nmtui printed nothing, you are on the usual Ubuntu Server / systemd-networkd setup. List the plans:

ls /etc/netplan/

Open the Wi-Fi file you made before (often 10-wifi.yaml, sometimes the installer name):

sudo nano /etc/netplan/10-wifi.yaml

Find the password: line under the house SSID. Replace it with the new passphrase. Keep the quotes. Keep spaces for indent — no tabs. Save.

Shape reminder (fake password, swap interface and SSID to match yours):

network:
  version: 2
  renderer: networkd
  wifis:
    wlp2s0:
      dhcp4: true
      access-points:
        "HouseSSID":
          password: "example-new-pass"

Apply from the keyboard (you are at the screen, so a rollback timer is optional):

sudo netplan try

Or:

sudo netplan apply

Never joined with netplan at all? Use the full first-join walk: put the old PC on house Wi-Fi.

Step 4: confirm a house number, then SSH

On the computer:

ip -br addr

Or:

hostname -I

You want a house address on the radio line. Ping the router (swap GATEWAY from ip route, the default via line):

ping -c 3 GATEWAY

Three replies mean the new passphrase worked. From the couch, find the number and log in: find it on the house network, then SSH from the couch.

If the house pointed DNS at this computer for Pi-hole, ads should calm down once the radio is back. Still messy after a gateway swap? When the ISP swaps your router. Ads only, with SSH fine: when ads come back.

Step 5: if the SSID changed too

Some ISP resets rename the Wi-Fi (new HouseSSID, not only a new passphrase). Then editing the password under the old name is not enough. In nmtui, add or activate the new name. In netplan, change both the quoted SSID and the password, then sudo netplan apply. Same idea as a first join on a new name: put the old PC on house Wi-Fi.

What this is not

This is not a mesh kit, a new router, or a USB Wi-Fi dongle. It is not the first-time join note. It is not a flapping-radio walk (power save and signal). It is not forwarding port 22 so SSH “works” while the radio stays offline. It is not dual-homing Wi-Fi plus ethernet as the plan.

What next

Prefer a cable when one can reach: a cable beats Wi-Fi for the computer, then keep Wi-Fi off after a reboot. Radio still flaps after the password is right? When house Wi-Fi on the old PC keeps dropping. Still hunting the number: find it on the house network. SSH odd with a good link: when SSH won't connect. Whole gateway replaced: when the ISP swaps your router.

Optional: jot that you updated the lab Wi-Fi passphrase (and the SSID if it changed) in Lab plan — username + passkey, no email. Skip if you just want to keep reading.

Skip

• Skip a mesh kit or a new router for a wrong saved passphrase.
• Skip a USB Wi-Fi dongle before you edit the password once.
• Skip forwarding port 22 to paper over an offline radio.
• Skip this if the computer already lives on a cable with working SSH.
• Skip this if the radio never joined once — that is put the old PC on house Wi-Fi.
• Skip guessing the passphrase over a dead SSH session. Sit at the keyboard.
• Skip pasting the house Wi-Fi password into a chat.