Hi Ian, The symptoms sound like it needs a good service, the heater clogs up with carbon and they usually need carbon blasted to remove it all. We recommend you have the heater serviced once a year to ensure it works for a long time. There is a dealer search on the Eberspacher website: http://www.eberspacher.com/dealers/dealersearch.html Nearly all of these dealers have the capacity to service your kit, or we can do it for you but you will have to arrange getting it sent to our Manchester depot. Thanks.