Altered header pressure resulted in reduced capacity

[Boobah]

I pressed the ball down to allow as much water before reaching overflow pipe. Depth 8”/20cm. No water exited the vent.

If i did extend the vent higher all i’d be adding is a pipe with air in it….

Edit the knurled cap is a lid, a white blank under it in the ball valve assembly.

 

[trojanhawrs]

Think you try your original plan of upping the cold water feed to hot tank and take it from there. Let us know how you get on