You could try a limefighter and/or filter strainer on the cold feed to the cistern.
And I take it you're not using blue loo or some other cistern cleaner in the tank?
Have had this once before but was hidden when re-siliconed!
Cutting old silicone out and handle of knife against the tile has left a thin black scuff mark along the length of the screen profile! Didn't even apply a lot of pressure and the part that made the mark was plastic!
Is it a scratch...
It's about resistance and the pump's ability to ensure flow rate suitable for all rads on the system.
22mm carcassing with 15mm loop offs is always much better.
Yes. You have to do what you have to do.
However.... Beware if it will pass behind appliances as these now normally go all the way back to wall with no service space.
Wonder if the vado pop-up is all plastic mechanism?
Tbh, having installed hundreds of them, it's never occurred to me, until now, that stepping on the dome could damage the mechanism!
Yes. But depends how big the hole is and how much is crossing over! But generally, this is a sign... As is cwsc filling up if no hot water is drawn off.
Well. He spent 3 hrs on site and is a plumber. So he has a much better handle on it that anyone else.
It's down to you and your faith in him.
That's the nature of things.
Life don't come with a guarantee.