My late mother's house has a Baxi Bermuda back boiler, a gravity-fed hot water cylinder, a Honeywell ST6400A 7-day programmer, a room thermostat and some TVRs.
The house is empty for weeks at a time and, when I left, I used to turn the programmer to OFF for hot water and to AUTO for central heating with the thermostat down to 10 degrees thinking this would give frost protection to the house. (Setting the controls like this also meant that when I was going to stay in the house, a neighbour could simply come in and turn the thermostat up so it was warm when I arrived.) I have now understood that the central heating won't work unless the DHW is on so doing this would never have had the desired effect in terms of frost protection.
I still would like the house not to fall below 10 degrees as I believe it would be bad for the fabric of the building (and it would take longer to get up to a comfortable temperature when it is occupied). However, I don't want to heat hot water when the house is unoccupied.
Is there any (inexpensive) solution which would enable me to have the central heating come on without DHW?