Ah thank you for your concern peeps.
I am pleased (well ecstatic really) to announce that I have cured the problem and have central heating again.
The freezing cold job of sitting on a garden chair, crossing my fingers the hair dryer wouldn't burn out, whilst I defrosted the naughty pipe was worth it in the end.
I have never been so pleased to see a lump of ice plop out of my pipe.
I shall make sure I run the hot tap at regular intervals to keep that naughty pipe ice free.
My next job is to make sure I cook something hot and yummy in the oven to celebrate my lucky fix.
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Hurrah! I think relief is my favourite emotion.
Glad it's sorted, and at your own (freezing) hand, so satisfying.