I ran the tap and checked all pipes to be sure I hadn't got the wrong one and only one pipe heated up.
By your post, I think that's the heat exchanger found out.
Thank you!
I found a post on here with a similar problem and have been advised to start a new thread as this is for a different brand. This looks a very good site!
We are having a big problem with hot water supply to taps and the shower, especially upstairs.
Hot water will heat rapidly then go stone...
What was the result of the visit, please? We have been having exactly the same from a Vokera Unica HE.
We are in a hard water area, so after some tricky searching I suspect the heat exchanger...