Sorry to see all the issues you are having and thank goodness you have got posters on here who know what they are talking about, plus you are pretty knowledgeable to start with.
For a fleeting moment I thought about getting other quotes for our replacement pumps but seeing all the issues you are having I think it is best to stick with an installer who I have confidence in rather than searching for different manufacturers/better price.
We have a buffer tank in an outbuilding where the boiler is also, the engineer is going to remove the boiler and move the tank, it might be possible to swap the tank for a larger buffer tank, as it doesn’t seem that large, is that something I should consider
