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Thanks for all the replies and recommendations. We are investigating the issue. I will post our conclusions once we have some results. Hopefully it will be helpful to someone

pipes are insulated, the rest i will have to check when I have time next there are some really good points

I know

Thanks again for the feedback. I wouldn't say I didn't take an interest but thanks again, you might be right.

The entire system had to be replaced. HW tank and everything was installed by him/his company. It physically can't be that long. Will do that test in the coming days and see how much it is.

To be fair, we don't know who is at fault. The ASHP installer didn't advise the plumber on the requirements apparently so they just did what they always did. One could assume the plumber might ask but he didn't. On the other hand we were advised that under the certification scheme it is a requirement for the ASHP installer to advise the plumber on the system needed. That did not happen

Thank you, that's good input - our problem is that nobody is trying to figure out the issue or is willing to admit a fault. We are currently trying to find some sort of independent surveyor to assess what's wrong...

Unfortunately, the pipes are already behind closed walls. We had full trust in the system until we started living in it. I will inquire about insulation to the pipes though, that should have been done for sure. We need to see what can be done at this stage... Thank you!

There is a pressure vessel nearby so assume it is an unvented hot water cylinder...

Thank you, I was thinking of doing that. Also good point on the pipe sizes - will check on that as well. Thanks a lot - that has been very helpful already

Thanks a lot OK, Would need to check that. There is a distinct difference from hot water to cold water pressure which should be one indicator of the issue

Thank you, that is a very thorough estimation. I would estimate the pipe in question to be 8m, so roughly half. Our water pressure is quite low compared to previous experience - or compared to neighbours. I always assumed the ASHP doesn't take away from the water pressure, so not sure anymore what the culprit might be. What I am mostly annoyed about is less the inconvinience but more about how much water we will be wasting in the long run...

The hot water tank is below the shower, maybe 3m over from the tap. So not too bad. Thank you for the comment on pipe size.

OK, that is good to know. I assumed that is the case from different discussion I have had. The 28mm was mentioned in a few articles I have read. We are basically trying to figure out how to improve and those were the points we could find.

Hello, Firstly, I wanted to say thank you to anyone being able to help with this. We undertook a complete retrofit of a Victorian Terraced house. Since it was in very bad condition all the plumbing and heating had to be replaced. We took the opportunity to install a LG Therma V heatpump. We were very relieved to see that the house is heating up well through the UFH BUT very early on we noticed that it takes 2 mins for warm water to arrive in the shower one floor up from the GF plantroom. The upper floor closely to 3mins. We wouldn't mind that if we are talking about an old house - but this is essentially all new! We discovered meanwhile that 1.No return pipe had been installed and 2.All the pipes all have the standard diameter of 22mm instead of 28mm. We are not experts but are currently trying to figure out what the issue would be. The plumber is saying a return pipe to the existing water cylinder is not standard and that's why he didn't install it and the heat pump contractor says that he was only there to install the heat pump, nothing else. Any advice or experience in that matter would be much appreciated. Thanks in advance!