Bill wrote:

After using a lot of hot water, the pipes have run dry. There was a
gurgle and then a hiss like air being sucked in - then the hot water
went off.

The hot tap works in the kitchen downstairs, it's just the bathroom
taps that don't.

I left them alone for an hour or two then turned the sink tap on
again. There was a weak flow of water then it went off. Same with the
bath.

I don't have a hosepipe to try the trick of forcing water up from the
kitchen cold tap, nor do I have any plumber's tools.

Any suggestions, other than call a plumber?

Do you have a plumbed in washing machine? If so the hoses on this can be
used to connect between hot and cold supply. Assuming you have a cold
water tank in the loft with an overflowpipe, connect hot and cold, open
washing machine valves ubtil overflow runs, then open hot taps one at a
time until all flow. turn off machine machine valves. Job done - or
should be!

Good luck

Bob