smart device dropping connection to remove server - ASUS RT AC87U Merlin


New Around Here
Hello All,

I'm new to the forum and thought someone here would have a better idea than myself about resolving this issue.

I'm working with an ASUS RT-AC87U running Merlin which is working well for the most part, except for one smart device that controls underfloor heating which drops its connection with an external server after so many hours preventing control.

The UF heating device is in a separate building and connects over WiFi to the LAN via a BT HH5 configured as an AP only (all networks serviced are passed to the ASUS router).

From what I understand the remote server has a dynamic IP and uses a hostname for connection alongside a DDNS service.

My WAN is configured to use Privacy DNS (Quad 9) and DNS over TLS and works fine for all devices on the network.

If the router is rebooted the service will connect to the UF heating device, however after so many hours the connection is lost, which probably occurs when the server gets a new IP.

I've tried routing the DNS queries for the smart device through the ISP DNS servers directly using a DNSFilter.
I've also tried disabling DNS rebind and secure UPnP and port forwarding/port triggering using the devices main ports 80 and 443 which I have been told the device uses all of which make no difference long term.

Any ideas on how I might be able to stabilise this connection once and for all?

UF heating provider will not give out server details so unless I put a traffic sniffer on the network I'm not sure the details I have been given for the UF heating devices' connection are 100%.

Thanks for reading this and all advice/ideas welcome.

Last edited:


New Around Here
About 15mtrs Greg72 so there shouldn't be any signal degradation and I've got a CAT6 cabling infrastructure that is sound with other devices on the same leg that don't have connection issues.
The device remains on the LAN (visible, addressable etc.), however it drops the connection with/to the external server (or vice versa).

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