Hi,we had this fire fitted almost 3 years ago. It has been regularly serviced but lately it goes out. When it is set in the high position it's okay. When it's turned down it may be ok for awhile untill someone opens a door and then it will go out a few minutes later. I regularly vacuum behind the grate to stop a build up of dust. The burner and thermocouple look okay to me. No build up of sooty deposits. Would be most grateful to know what might be the cause when I call out the fitter.
Thank's in advance.