It is true the WB engineer is only responsible for the workings of the boiler, however at the time when we had called WB out we were trying to get to the bottom of the issue as at this point we only have the hissing in the rads and the chattering at two TRV's. Also our installer recommended we get WB out to get their take on things as he didn't have any thoughts on the matter. Its laughable when I type this that a gas engineer who is WB accredited with 30-40 years experience cannot figure out what is going on or even shed any light as to what is causing the issues.WB engineers are there for the WB boiler, not the system. I'm surprised they would even touch the system once they've deduced that the boiler is performing as it should.
Maybe they didn't! But just commented on it instead!
What you really need is a decent independent heating engineer and plumber who can look at the whole system.
I think when WB came out is was to appease me the third time, albeit WB have really gone down in my estimations after rolling out the 4000 from the factory without a vital update which meant it took two sink full of water before you got warm water. A known issue that they let slip and hoped customers would not notice.
My issue is finding a decent gas engineer that knows his stuff, when you don't know enough about what they are telling you then really its hard to know unless its obvious if they are spinning you yet another pile of rubbish.