Owning your own home

I know this is a mildly contentious issue (boilers/plumbing) so I apologise for bringing this back up, but given that I think a couple of people on here have experience, I'm just looking for some advice.

My boiler had a water leak, water was dripping out at the bottom, but other than that it worked perfectly fine. After a few weeks, the water pressure would drop enough that were was an error and I'd open the valves to refill the pressure and it would resume working fine.

I called out a heating engineer and they diagnosed a leaking diverter. They ordered the part, came back to fit it and also serviced the boiler because it had been a number of years since it had been serviced.

Since they fixed it, it now struggles to maintain constant hot water and hot water pressure out of the taps has dropped.

This is manifesting itself as:

• If I turn on the hot tap on the bath and the shower, whichever one I turn on 2nd gets barely any flow. This isn't exactly a normal use case I acknowledge but I sometimes do this for 20-30 seconds when turning the bath on for my son's bath to let the bath tap get up to temp and to rinse off any residue/dust/hair in the bath before I lower the plug. I used to be able to do this fine and now I can't.

• Overall hot water pressure seems lower although this is subjective, I can't be sure.

• The boiler can't maintain a constant flow of hot water. After a minute or two the water goes warm and stays there for about 30 seconds then goes hot again.

• Once or twice, when I've been in the kitchen I've seen 1p1 error flash up on the boiler then disappear, but not in correlation with the above issues. A quick google shows "insufficient circulation" as the description of the 1p1 error.

I messaged him after a couple of days, I don't have hot showers so I didn't notice it and it took a couple of days for my wife to bring it up. He messaged me back to say "it's most likely a coincidence, if anything it should work better than ever", but he did say he could come round and have a look. Since then he's not replied to nail him down on when he's coming round and he didn't answer when I called him.

I'm just trying to work out whether it is a coincidence, in which case I'll just call someone else who will come fix this problem and not ignore me, or whether they are related and I should chase this guy up.

I understand that this could be a pre-existing issue and that by fixing the diverter it caused this issue to surface, I'm not looking for a free ride here, just seems incredible coincidence.