Viktoria - I have a similar problem with a sink too far from the boiler - in Summer I catch the spare water for the garden! I have wondered about a small water heater, but I think the electricity might be a problem. (But then I always see the problems.

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I have just sent my diary in, and reading through the previous ones I have discovered that I always seem to plant out my tomatoes in the green house near this date, and also that there has been at least one other year when I am still hanging on to my winter duvet in mid-May.