The heating system sprang a leak last week. Nothing serious; a fibre washer had perished and water was seeping past it. The difficulty was that I had turned the boiler on (to heat the pool for guests) and didn't really want to turn it off until they had left in a few days' time.
I turned to that wonderful modern aid to DIY, mastic; in this case, a plumbing jointing compound that I bought from Wickes when I was last in England. I can't seem to find it in France. It says you can effect a temporary repair if you take the water pressure off, smear the mastic onto a bandage and wrap up the leak. Well I couldn't take the water pressure off without shutting down the boiler, so I just wrapped it up. It worked. The leak was reduced to a slow weep and the pressure lasted through the weekend. Today I did the fix.
The washers are a non-standard size that I can't find in DIY shops, so I had to call in on the plumbing firm that did the original installation, who gave me some for free (thanks, Lecoq).
There are two joints of the same type in the system, so I re-did both at the same time, just in case, using also the same mastic jointing compound that did the temporary repair. Here they both are with their bright new green washers. I'll put the water back in the system later today or tomorrow.