We are currently havign a few issues with a friends Heatline Vivo boiler. We are thinking of having it moved to the other end of the kitchen whilst we get the faults fixed, may as well do it all together. However we had an RGI guy out today to quote us for this work and he who said we cannot re-use the flue, we will need to get a new flue. Is this true, and if so, why?