HG612 hanging

[#1]

I had FTTC installed about 18 months ago, with sky and now plusnet.
The openreach supplied HG612 modem has started hanging occasionally. I have an ethernet connection to the modem over which I can telnet. When hung I have no net connection and the modem doesn't respond on telnet. If I cycle power to the modem the net connection comes back and I can telnet to it.
In the past I have had the modem report 150+ days of dsl uptime so either the firmware update(s) that BTOR load have made it flakey or the modem is starting to die. It is the 3B version which isn't supposed to suffer from overheating problems and it is mounted vertically on a wall anyway.
Who's problem is this? Is it up to BTOR to replace the modem? It crashed a couple of hours ago and 5 days previously so it isn't a terrible problem (yet).

[#2]

The modem belongs to BTOR so it's their responsibility to replace it.  You'll need to go through PN to arrange though.
Of course, as you've hacked your modem, BTOR might charge you for interfering with their equipment so you'll be removing the cable to the second LAN port and keeping quiet about your diagnostics when the engineer turns up with a new one won't you 

[#3]

Or just get a replacement  hg612 or an  unlocked ECI  from that well known auction site....
Far less hassle waiting around for an openreach appointment + you could be landed with a £££ bill as pwatson notes for interfering with their equipment.