No trv's were changed with the boiler but one was added later to replace an old leaking valve. Could this cause such a loud noise even when the central heating has been off for 10 hours+? With apologies for my ignorance....
No it does not coincide with the toilet being flushed or any other use of cold (or hot) water. There was an earlier problem with water hammer when the toilet was flushed but that was a completely different noise/vibration and was resolved with an arrestor.
I had a Potterton Promax Combi 28HE+ boiler installed in Nov 2011. In Feb 2012 I had a couple of central heating pipes replaced which entailed the system being drained twice. After 2 weeks pipes started vibrating extremely loudly - it sounds like someone drilling through metal and fills the...