Santon Premier - Vibrating noise

[TMG11]

Hi, we have a santon premier unvented water heater that we are struggling to diagnose an issue.

When drawing hot water we are sometimes getting a banging noise similar to water hammer, we have changed the PRV after the main stop cock and we have fitted an arrestor as we initially thought it was water hammer - the noise is still present, plumber is scratching his head as am I!

Its particularly noticeable when the system is or has just finished heating water and we draw hot water, it happens from any tap initially, but if we close the tap and then re-open the noise doesn't reappear - any help appreciated if you have seen this issue before

 

[snb1]

your plumber should be G3 qualified to work on these as they are a controlled service. If he is qualified he could sort this easily. Afraid we can't give advise out on controlled items

 

[TMG11]

Our plumber is G3, he’s scratching his head with this so looking for any useful pointers to help - we’ve now just changed the cylinder and the issue is till happening - any pointers would be useful, clearly he’s not going to do anything crazy

 

[snb1]

Replace expansion vessel

 

[TMG11]

We have replaced that yesterday and we still have the issue