Developments from today:
I contacted customer support via chat. I had all the information to hand; serial nrs of the heatlink and the thermostat. I confirmed that I had tried all self help advice available for fault H71 to no avail. I was then told I was eligible for a free heatlink replacement.
I was given 2 choices: visit the BOXT website and organise for an engineer to come and replace the unit, or have one sent to me and have it fitted (cost of fitting reimbursed later). I opted for BOXT. I went to their website and but there was an issue with their booking service so I called them. Very helpful. I was told an engineer could be with us the next day (tomorrow) - much faster than I anticipated. Later the same day (today), I got a call from BOXT saying they had an engineer in the area so he could pop round and get it sorted. So it's now all sorted in less than 12 hours of reporting and I have a working heatlink.
Probably just good timing and luck, but I'm impressed - not often you can say that about any customer service.
