While anti-freeze will protect your heating system, it will not protect the water supply pipes for drinking, washing and toilet flushing. You need to take action to prevent those pipes from freezing and bursting.
In prolonged cold spells, porcelain fittings can also be damaged if the water in them freezes.
It's seldom possible to fully drain any heating system. There will be low points that cannot be accessed. The best strategy in my opinion would be to dose the system with a central heating inhibitor that includes anti-freeze and run the system at a very low setting between 5 and 10C. It is also important that the system fires up regularly to make sure the pump doesn't sieze. Modern boilers do this automaticaly once a day at least and many have built in frost protection. As you are absent from the property you will also be unable to correct any faults due to power interuption so anti-freeze will help you in this instance too. I'm a heating engineer in the U.K. during the winter and live in France during the summer.
Hi Jo
I agree with Glen that antifreeze would be the best option, I worked in the heating industry for 40 years and prior to the development of suitable products draining systems was the only option.
I use a company in the uk for a lot of stuff I can’t easily get here and they are cheaper.
http://www.bes.co.uk/product/108~PL~1902~1902~-Fernox-Inhibited-Anti-freeze-.html
They deliver free in Europe for orders over £40 or minimal postage for orders under.
Never use antifreeze designed for cars it’s toxic.
Whether it is possible to fully drain your heating system will depend on the design quality of the installation.
In France, pipes are often hidden behind plasterboard, so less well insulated than a completely internal system.
But 500€ would pay for a lot of plumbing repairs if you did get a burst (so long as the main supply is turned off).
I suggest that you take a look at your system and make sure the frost-protection system is controlled by an appropriate outside thermostat.
Maybe the cheapest option would be to turn the main heating off, get a few electric fan heaters and leave them on the frost-protection setting.
There are so many variables - construction of house, location, quality of heating installation, etc. So every case will be different.
But the most important thing is to turn off the main supply when you are away from home. Some relatives in Atlanta took a short holiday over Christmas and returned to find that there had been an unexpected cold snap and their house had become an 80,000 gallon swimming pool. Fortunately they were insured, but it's still a lot of stress and upheaval.
I think you would be best paying someone a small retainer to be "guardian" of your house. This person could then switch the heating on for you if there was a large minus in temperature and turn it off when the thermometer rises. I havd friends here in the Gers who do such work and I'm sure it wont cost you €500 a winter. The same person could also then open up your house for you before you return and probably get you some milk, butter and bread for your return here.
You could use anti freeze in the system. you would need to work out how many litres in the system and then add it in through a radiator vent. It is not cheap but probably cheaper than keeping the heating on and will also aid the system as it will have anti corrosive mixed with it. The problem with draining down is you introduce air into the system and this is bad. i.e water + iron/steel + oxygen = RUST.
Regards Alan
We are slightly north of you but in the infamous 2012 cold snap the temperatures stayed well below zero for two weeks here and although our system had been drained we lost 12 out of 14 old cast iron radiators which ended up çracking in the cold. We knew others who had the same problem and our insurer, who paid, said they had several other claims in our area. Cold snaps like that one are pretty rare in Dordogne and Charente but do occur occasionally so probably best to take some precaution.
Hi Jo, we too leave our house for the winter and we don't drain our rads (most are the heavy steel old fashioned ones). We leave our heating off but it does have an 'hors gel' system so it would kick in if the temperatures really plummet. We are in the north of the dordogne between Montpon and Mussidan but still do, at times, experience very low temperatures. I made the mistake one year of leaving the boiler on and turning the thermostat down but to my horror the thermostat stopped working and the house was like a hot house upon our return, not to mention a near empty oil tank!!! These days we do make a couple of trips over to the house during the winter months and have a reliable person who we pay to pop in once a week. We have never had a problem with burst pipes etc but the house is double glazed and very well insulated. Hope this helps.
Angela
I suspect you have your internal thermostat set too high.
I agree with BM that draining all the radiators is a bit of a pain and you will need to replace the inhibitor when you refill them which is an additional cost. You may get away with just draining partially so that an expansion air gap is left in at least one radiator on each "loop" but you will need to be sure you have covered all the loops. Sometimes you get "inverted loops" in the pipework which can be very difficult to vent thus making the system noisy and inefficient when it is running.
Of course if you are only in France for the summer you could drain the whole system down and leave it empty with no problems. Otherwise maybe resetting you internal room thermostat to (say) 4 degrees C or even a bit less as long as its in the coldest part of the house would cut the cost of keeping in on standby a lot. I agree with BM that if the house is reasonably well insulated it would need to be a lot colder than -4C to freeze the pipes inside.
HOWEVER if you did have a burst pipe your insurers would probably not pay for any "flood damage" if the whole system was not drained or on "standby"
We are not far from you. Unless it is an exceptionally cold winter there is no need to drain well lagged pipes in this area. There is no way radiators would freeze indoors with an outside temperature of -4, even with that indoors. We have had -12 last year but because we live here kept the water on of course. No problems. A couple of days a few winters back touched -20 something overnight and then the water was frozen but perhaps 24 hours maximum. If you are being advised by somebody living on high ground such as the Pyrenees or Alps then ignore it and just go by Dordogne temperatures.
Apart from that, if you have old fashioned radiators using the mains water system rather than enclosed ones, drained radiators are troublesome to refill. Airlocks, 'bumps' and bubbles for months as we know from when we had a new boiler and stove installed. We have one radiator that does not fill after four years as a result, fortunately not one that matters. There are lots of myths, ignore them.