Water flow into the toilet!

[balloney]

In the past week when the toilet is flushed in the morning, the water closet starts to overflow. During the daytime it is normal.

During the night does the water pressure change ?

The water closet is a Forham and has a Torbeck Bottom entry Ballvalve.
I have noticed that when it does go into overflow the Ballvalve still lets
water in.
Why is this ?

[Sipowicz]

It sounds as if there is a piece of grit/sand /dirt on the diaphram, stopping the ball valve from fully closing. The water pressure makes difference. It just needs taking to pieces and cleanig. Most DIYers are capable of this.

[The Builder]

It may be dirt Balloney, but often it's just that the float level is set too high. It's easier to adjust the level with a Torbek.
Overnight, pressure rises quite a lot, simply because fewer people are using it :o)