To clarify Gas valve was replaced and fitted by Vaillant engineer.
Flue fix was done - 24 hours so far, no leakages. Surprisingly, since the fix the vibration noise occurred only once and for a very very short amount of time : 2-3 seconds tops. before the fix - the noise was louder & lasted WAY longer > 10-15 sec. 'Simond' - on this thread had suspected this to be the problem. well its not resolved but definitely reduced
I agree with Tony when he says that Vaillant guy didnt want to get involved at all just because he saw the dark water. he has gone back and written a report that there were 1000 'ppm' in water. I don't know what 'parts' were these and how did he arrive to such a precise number. all he did was to collect the water in a plastic bucket and showed me - "its dirty - get a power flush" & left
There are so many issues and things that are missed, I am surprised this guy is still being allowed to look at the boiler ........
your points are all carefully thought of, thx. Did i select the installer out of cheap quote? Nope. I am in a purpose built block of flats and this person has done A LOT of boilers in this property. people have been happy & didn't hesitate in recommending. I will speak with the person who signed off his work tomorrow. Flue work as told to me is in line with a 3 degree slope to the boiler. for most part of the flue, its a straight line with one elbow point where the issue occured. I hope you can appreciate that I cant guarantee that slope is correct, I do have to take installers word for it. I am not going to let that installer any where near. previous boiler was fine, the old flue had developed a leak. as that boiler was about 14 years old, i decided to go for a completely new setup.
Thanks a lot for all the replies. here is what I am thinking.
1. Hearing from all of you - the first step is to get the flush done. I am tempted to go for powerflush and magnaclean and will of course hire someone else to do this.
2. Review flue work - I can ask the engineer who signed off to come and review OR hire a new engineer. Again I am tempted to hire someone else.
3. Once Point 1&2 are done and if noise is still a problem, make the video as suggested and ask vaillant to get in for inspection & take it from there.
Thoughts?