Thanks for the help, once we have found a plumber our only problem is accessing the pipework which has been plastered in, but that's a problem for another forum...
Interesting comments about plumbers; in fact we moved in to the house only 4 months before the problems started, and I suspect...
Can anyone suggest what my problem might be? Our Ravenheat gave up the ghost on Good Friday (of course) and we payed £150 for it to be repaired (though there seemed to be nothing wrong it still took 1.5 hours to clean it & put it back together again;we were just happy to have hot water again!)...