Home Assistant Opens Locally but Fails Remotely After a Router Change

Eva Wong

IceWhale author

Eva Wong is the Technical Writer and resident tinkerer at ZimaSpace. A lifelong geek with a passion for homelabs and open-source software, she specializes in translating complex technical concepts into accessible, hands-on guides. Eva believes that self-hosting should be fun, not intimidating. Through her tutorials, she empowers the community to demystify hardware setups, from building their first NAS to mastering Docker containers.

Home Assistant Opens Locally but Fails Remotely After a Router Change

If Home Assistant still opens on the local network after a router change, Core and the basic LAN path are probably healthy. The failure is more likely in the new router's address assignment, NAT rule, public IP, DNS record, VPN or tunnel route, or reverse-proxy path.

Do not reinstall Home Assistant to fix a remote-only failure. Prove the local address first, then move outward one boundary at a time until you find the first place where the new network no longer matches the old remote-access design.

Confirm the New Router Did Not Change Home Assistant's LAN Address

The new router may use a different subnet or may assign Home Assistant a different DHCP lease. A port-forward rule copied from the old router can therefore point to an address that no longer belongs to the Home Assistant host.

Find the current address in the new router's client list or Home Assistant network settings, then open that exact address from a device on the LAN. If local access works, create a DHCP reservation if you depend on a fixed internal target for NAT or reverse-proxy routing.

The ZimaSpace guide to separating LAN-IP changes from public-IP and DNS changes is the right first boundary after replacing a router.

Rebuild the Remote Entry Path for the New Router

If you use direct port forwarding, recreate the rule on the new router and verify the target is the current Home Assistant LAN address and listening port. If you use a VPN or outbound tunnel, confirm the connector is online and that the new router is not blocking the outbound or return path it needs.

Home Assistant's remote-access guidance distinguishes Home Assistant Cloud, VPN, reverse-proxy, and port-forwarding paths. A router replacement affects these methods differently, so troubleshoot the method you actually use instead of copying an old NAT rule into a VPN-based setup.

Test from cellular data or another truly external network. Testing the public hostname from inside the same LAN can be confused by NAT loopback or split-DNS behavior.

Check Whether the Public IP or CGNAT Situation Changed

A new router installation often coincides with a new WAN lease, modem reboot, or ISP provisioning change. If your public IPv4 changed and dynamic DNS has not updated, the hostname can still point to the old connection.

Compare the WAN address shown by the router with the public address seen from the internet. If the router receives a private or shared carrier address rather than a public IPv4, direct inbound port forwarding may no longer work because the ISP's CGNAT sits upstream.

Do not keep editing Home Assistant when the new router does not own the public NAT boundary. Use Home Assistant Cloud, a mesh VPN, a reverse tunnel, or request a public IP from the ISP instead.

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Verify DNS and the Home Assistant External URL Separately

Resolve the exact hostname used remotely and confirm it returns the current intended public or tunnel address. Then test the destination directly where possible. DNS success does not prove the proxy or port is correct, and a working port does not prove the hostname resolves correctly.

The Companion app can use different internal and external paths. Its current networking documentation covers internal URLs, external URLs, DNS, IPv4/IPv6, and reverse-proxy behavior. A router change can expose stale settings that were invisible while the old network happened to match them.

If the app fails but a browser on cellular works, compare the URL and network profile used by the app before touching the server.

Recheck Reverse-Proxy Trust Only If the Proxy Path Changed

A new router can also change Docker subnets, proxy addresses, or the machine that terminates TLS. If requests now arrive through a different reverse proxy, Home Assistant may reject forwarded headers until the new proxy is trusted.

The HTTP integration requires trusted proxy configuration for traditional reverse proxies that send X-Forwarded headers. Do not widen the trusted network to the entire LAN just to make the error disappear; trust the actual proxy source.

At this point the failure should belong to one layer: wrong LAN target, missing NAT/tunnel route, changed public address, CGNAT, stale DNS, or proxy trust.

FAQ

Do I need a new TLS certificate just because I changed routers?

Usually no. A router change does not by itself invalidate a certificate for the same hostname. Certificate trouble appears when the hostname, challenge path, proxy, DNS, or TLS termination changed.

Why does the remote URL work on mobile data but fail on home Wi-Fi?

That points to an inside-only routing or DNS problem such as hairpin NAT or split DNS, not a general remote-access failure. Test the internal DNS answer and proxy path separately.