Draining Water System

For what it’s worth, many years ago, I used to have to leave my flat in Bath unattended for months on end while I was working away in South America. Often over winter, and the same thought occurred to me. Rightly or wrongly, I used to leave the central heating programme running but turned the thermostat down to 10C. Theory was that if the weather got cold enough to freeze the pipes it’d also be cold enough to trigger the boiler.
May not be recommended but it must have worked as I didn’t have any problems.

Might it cost less to have a thermostat installed than to decommission and reinstate the whole system? Similarly to Humph, I found using that protective setting in the now-sold parental home in Sussex was enough. Good thing too, as once the house was empty, the insurer imposed a condition excluding any claims relating to burst pipes.

Further thought: you could also put some thermostatic fan heaters in strategic places, away from anything combustible, and control them with timers, or remotely with a smart plug system like Tapo — although that does require a network connection of some kind.

Strikes me that any purchaser is likely to replace the system anyway so I wouldn't worry about draining it totally and then having to refill with inhibitor etc. Just drain and forget and just let any purcahser know what you have done.

So a new heating system would be required anyway.... Drain it fully.

As per our resident professional I'd get it properly drained so that even if the internal temperature fell massively below zero for days there was no prospect of damage. I think, if you were not going to refill and re-commission shortly before completion, you'd need to be crystal clear via your solicitor/conveyancer that the buyers need to sort that.

We moved into a rental c1990 that had been drained down but as the space heating was Gas Warm Air no rads/headers etc were involved. Landlord sent a plumber to meet us on move in day and he refilled the HW system. It was supposed to heat directly through an adjunct to the warm air system but that wouldn't stay alight. Probably scaled up as the local ironstone clogs lots of things. Ended up with the LL providing a longer a longer and better immersion heater and we used Economy 7 electricity for hot water.

Note what you say about lack of activity by your buyers on searches and, more worryingly, fact this is not registered land. Son and daughter have both been messed around by either sellers or buyers who seemed not to understand what was required of them. I blame the modern tendency to go cheap for conveyancing. Keeping the client in the loop and explaining stuff seems to be one of the 'extras' that's gone out of the window to keep costs down.