Tex: Difficult to see, even blown up, but have you got one of these between the boiler ports hot and cold? It's a mechanical bypass [vanne melangeuse suedeoise- never seen one in the UK], with a dial indicating the amount of boiler hot to cold bleed-back. They come in 3 port [voie] versions too. They do tend to gum up solid, so adjusting the bypass is often impossible after a few years.
http://www.ebaneo.com/gamme-1820-vanne-melangeuse-4-voies.php No, we don't. If I find the folder I'm going to scan the original schematics. The boiler loop is just boiler - heat exchanger - pump - boiler and a couple of ball cocks.
The heating loop didn't get any circulation at all, except for gravity, the pump shorted out the whole heating system.
The whole thing is non-electric, except for the pumps...
To clarify one thing: this is a weekend home. When it's occupied we set the timeclock to permanent operation and back to 2-3 hours a day when we leave.
Since the house is very small (65 sq. m. living area) the system does keep the house warm, even in -20C weather (slightly below 0°F).
The system probably ran 365 days a year from 1998 when it was installed until 2008 when we put it on a timeclock. Apparently the previous owner kept the house at a toasty 20C year-round because she firmly believed in the necessity of doing this to keep the house dry. It does work, but I guess she'd better spent the money on a damp-proof course in the brick walls rather than on gas.
