Protecting a Vacant Property from frost damage over cold months

DoneWorking

This is an update from my previous post from December 2025

A friend is trying to sell a vacant property.

It's unlikely the sale will complete until Spring 2027.

He has vacant property insurance .

He is trying to decide on what to do to prevent frost damage and burst pipes over the cold months beginning in Autumn 2026

Plus avoid issues related to dampness.

Option 1

Drain everything down and leave heating off

Option 2

Drain taps and mains water and leave gas boiler running 24/7

TRVs set to 2 or 3

There is no room thermostat

Option 3

Leave mains water on

And boiler setup as option 2

It's a small 2 bedroom terrace with people living on both sides

Which option seems best

The energy cost for running the boiler on those settings is about £140 per month

He lives near the property so can visit anytime.

He doesn't have a remote temp or elec supply monitor connection to his phone

But can see the energy use each day for the prior 24 hour period

IE on Friday morning he can see Wednesdays energy use

Should he ask the heating engineer to provide a wireless thermometer

Currently there is just a mechanical clock on the boiler with tags to set on off periods for the boiler

Thanks

user1977

What does his insurance say about it? I would be inclined to turn off and drain.

DoneWorking

https://forums.moneysavingexpert.com/discussion/comment/82112470#Comment_82112470

Either drain system or keep home at a set temperature if water supply not drained

horsewithnoname

set it to about ten degrees. But best is to ask the insurance company

FreeBear

Drain taps and mains water and leave gas boiler running 24/7

TRVs set to 2 or 3

There is no room thermostat

Good grief. A basic wired thermostat can be had for less than £20, and a Tado smart thermostat/timer for about £100 (plus installation). That would make a significant saving in heating cost and boost the EPC by a couple of points. Really no excuse, even if the property is being sold.

With a decent timer & thermostat, leaving the heating to turn on for a couple of hours in the morning & evening to say 16-17°C would keep the place dry and drive off any condensation. If a smart thermostat were to be fitted, you could set a baseline temperature of 10°C which would stop pipes freezing.

Oh, and leave all the TRVs set to max. Especially with a smaller property, having TRVs shutting off radiators can increase the propensity for the boiler to short cycle which kills efficiency. Also worth turning the flow temperature down to 60°C (or perhaps 50°C depending on the size of radiators).

If you can't/won't fit a decent thermostat & timer, drain the heating & hot water down along with the cold water pipes. Turn the gas off as well, and fix big signs everywhere warning that the CH and water has been drained. Leave a bottle of corrosion inhibitor next to the boiler as an additional warning sign (will be needed when the system is refilled).

WIAWSNB

It largely comes down to whether he wants to spend money or not. Or cost vs hassle.

Most unoccupied policies state a min of 15oC, afaIk, so that won't be cheap. If you wish to reduce the risk of mould and mustiness, the property should be trickle-ventilated too, so that's more heat loss and waste energy.

The alternative, as FreeBear describes, should achieve the same end result, but at no cost other than a plumber to refill and test the system. I would add, tho', that for the heating off/drain down option, to doubly make sure the house is ventilated - every single window cracked to 'vent', and internal doors wide open.

There is also a small but ongoing risk that a pipe or fitting just 'leaks' for no good reason, and a drained-down system would not only be less likely to do this, but not suffer a loss if it did. (I once had water come through my dining room ceiling when the plastic nut on the upstairs toilet's inlet valve spontaneously split.)

If the boiler is a heat-only type, with a small header tank in the loft, then I'd definitely say 'shut everything down and drain down fully', as you'd have to keep the mains on for that type, and a leak in the CH system would get replenished and could cause a big mess. A sealed or combi system has a limited water capacity, so far less likely to cause 'damage' if it leaks, and it can be run without the mains being on.

DoneWorking

Thanks for all comments

I'm going to suggest the following

Ensure boiler is topped up to correct pressure during the boiler service next week

Turn off mains water supply.

Drain hot and cold taps and leave taps open

Leave notices to inform people not to adjust taps or stopcock.

Pre Cold Weather Period

Get a quote for a wireless thermostat for boiler and install before cold weather kicks in

Set thermostat to fire up boiler when room gets too cold

What temp would be best

Where should he site this wireless thermostat

What should he set TRVs to

FreeBear

What temp would be best

Where should he site this wireless thermostat

What should he set TRVs to

TRVs should all be set to max - This will reduce the tendency for the boiler to short cycle as well as keeping the entire property at a consistent temperature. Some boilers have a parameter that limit the number of starts per hour to help with the short cycling problem.

Thermostat is traditionally sited in the hallway. If the property were occupied, many people take it in to the room they use most.

Unoccupied property, anywhere from 10°C to 15-16°C. Lower end will prevent frost damage, higher end will limit condensation (but no eliminate it completely).

DoneWorking

https://forums.moneysavingexpert.com/discussion/comment/82112986#Comment_82112986

So

Set thermostat to maintain say 15 degrees C

Set flow temp at 50 degrees C

Set TVRs at max

Will this set up use a lot of energy

user1977

I've lived in places where a constant temperature of 15 would have been luxury, it seems over the top if all you're trying to do is keep all the pipework above zero.

FreeBear

https://forums.moneysavingexpert.com/discussion/comment/82113409#Comment_82113409

With a fairly modern condensing boiler (especially if it does modulation), it shouldn't use a huge amount of gas. Using a timer to limit the boiler running to a couple or three hours a day will reduce consumption even further.

Bottom line - It depends on the exact make/model/year of the boiler. Something that should have been asked on the first page.