Leaking toilet cistern

[TolstoyAteMyHamster]

It's leaking into the bowl, so although it's not causing any damage, it means the Saniflo unit is being set off on a fairly regular basis. Which is noisy and irritating for the person in the flat downstairs, who can hear it through the night.

I marked the level of the water in the cistern after flushing, and can see it's gone down by around half an inch in a few hours. I assume - though I don't know - it's something to do with the washers. Is this something i can reasonably fix myself with a trip to a DIY store, or do I need a plumber? I have tools (some) and am reasonably good at simple DIY but definitely nervous about anything to do with water...on the other hand, if I can avoid getting a plumber here, particularly at the moment, that would be a win.

check that there is no grit or dirt stopping the flush from sealing back up.

Thanks. That sounds manageable. How do I do that? Is it as simple as just looking/feeling around the bottom of the unit?

Yup, where the water goes through.

What type do you have?
One with a ball or one with a cup I. The cistern?

It could be limescale build up that is stopping the filler closing off.
Try putting limescale remover in the cistern.

I have changed my cup type fairly easily myself following YouTube.

take the lid off the cistern and photograph the parts inside please.

look at the water level, and compare it to the line on the back of the cistern marked "level"

flush it

compare it again

leave it half an hour and compare it again

you can pencil your own line if there is none.

This is the cistern. I can feel (though it isn’t easy to access) what I assume is the sealing ring that would stop the filler closing off. There is a little limescale there though not much. My concern about limescale remover in there is that the Saniflo unit may not appreciate that - I know you aren’t meant to put anything other than the approved cleaner there. But would that work, perhaps? As I have a bottle of that.

The questions about "level" are to identify which of the parts is at fault.

The water level is going down by about an inch an hour.
It seems to be the unit on the left (circled in the photo) as if I fiddle around with it and hold it up after flushing the trickle of water into the bowl stops. So I guess it is that that is sticking somehow.

That's odd. The fill valve should maintain the level and prevent it going down. If faulty, however, it can overfill.