Firstly, this ****ing house!

My toilet is being freaky, about every 10-15 mins the cistern fill turns on for about 5 seconds and then turns off again.

The issue apart from wasting water is that it’s right next to my bedroom and it keeps me awake (I’m a very light sleeper).

What do I do? I can’t see or hear any dripping into the bowl, there’s no overflow outside and my neighbour hasn’t told me there’s water leaking through her roof so what’s going on?

Rough guess is the diaphram is knackered on the flush valve. Cheap as chips to replace the whole valve (around a tenner I think)

If the syphon/float valve is knackered it will continue to leak water and then keep refilling itself. There should be a check/isolator valve on the inlet – turn it off and see if it stops.

Stick some dry toilet paper to back of bog and see if it’s starts to wet. This almost certainly will be flush valve… Possibly you can take valve off and clean the rubber washer but so cheap just replace it. Sometimes the leak is so small you don’t notice it

Had this with one of our (push button) toilets.
Turned out the rubber flap (flush valve) had absorbed some water in the shape of little dimples.
Popped the dimples with a pin and put it back…. Never reoccurred after a further 10+ years.

(I didn’t know you could replace the flaps alone)

Yep, on ours the rubber seal around the bottom of the flush valve had limescale on it.
Bit of a clean every year or so and it’s fine.

Modern toilets are terrible for leaking. Old syphon flush toilets never leak, they just get harder to flush.

Paper on the back of the bowl is the correct way to check if it’s leaking, but intermittent filling is another symptom.