About 1 in 5 times when my boiler fires up, the clicks of the igniter cause the network to drop out.  I have tried relocating the cables without any job.  When I looked at the cable though I noted they were unshielded Cat 5 cables and felt really cheap.

I have ordered a bunch of ferrite core filters and a new Cat 7 double shielded ethernet cable.  When they arrive I will try the ferrite cores first, then the new cable.  I would ideally like to suppress the interference rather than protect against it.  If the cores work I will still fit the Cat 7 Cable however.

Cat 7 Double Shielded Ethernet 3M Cable.

5mm Internal diameter ferrite filters.

I will post more details once I test.