On 15 Oct, 13:05, Tom B wrote:

The simplest solution I suppose is a programmer with an easily changed
battery and a scheduled annual replacement of battery, say along with
the smoke alarm battery change, but my existing programmer flattens
the battery in the event of a power cut lasting just a few hours, and
then it's back to re-entering all the settings.

How about a battery-powered programmer (i.e. no mains at all)? I'm
sure they run for a good few years but, just as important if I
understand your circumstances and requirements correctly, the battery
changing procedure is usually as easy as that of a TV remote control
(certainly my Honeywell CM907 is as easy as this - and as Dave
mentions an MSF module is available if considered essential).

Mathew