Good morning, I hope all is well and yes its me again! Well the Ideal technician came round and could not find the problem. My flue is slightly under a concrete porch and the Ideal technician said this was the cause as air was not going back into the vent properly. I told the Ideal man that I had originally had one of the long flues fitted but because the boiler started booming from the start the installer came round and fitted a smaller one but the booming still continues. The Ideal technician was convinced the concrete porch was the cause as he didn't say the flue was fitted incorrectly or it was the wrong size. So I will arrange to get a friend to cut away some of the concete porch, it wont be a problem just an added expense to hire the equipment but I do feel if I dont get this done then Ideal wont come out again as to them this was the cause but the Ideal technician could be right. Also I had never heard my boiler boom when only the water was running and the heating has not been turned on but I did hear it the other day so I need to make a note of that. One other thing (sorry babbling on!), I was telling my sister about it and she said it had happened to one of her friend's boiler and after a few text messages it turned out to be the fan, now I know one of you gentlemen (Danny) mentioned the fan so maybe this is the cause as I think my sister's friend said it hasn't happened since and it all sounds very similar but that one of you guys mentioned the fan. Its difficult when you are a customer as I dont feel I can stand next to an engineer or technician and say I have been on an internet forum and then make suggestions what could be the cause as you hope the engineer/technician knows what he is doing (though my dad of 70 would be doing exactly that!) but if I have to call Ideal out again then I think this time I will say something as its driving me mad but also it is a bit embarrassing knowing that the boiler might go off when people from outside walk past as when outside it does sounds like a gunshot (just a boom indoors although the boom can sometimes sound a bit more of a "crackling boom"). But first I feel I will have to get my porch done first as I dont think at the moment I am in a good enough position to call them out again and say can you check the fan (though I would love to do so), as in their view the problem is the concrete porch and who knows it could be exactly that. So I will get on with things, see how I get on but will let you all know as I know you are so interested!!!! tee hee.