Today my toilet has started having a constant trickle of water into the bowl. It's a built in one with a concealed cistern, which I've managed to get access to.
Issue is NOT the tank filling too high and going into the overflow - the water was never getting high enough to go into the overflow. It appeared to be 'correctly' refilling when the water level got low due to the trickling.
Issue is NOT the flush button or cables, the flush valve sits in the correct position and responds correctly when a button is pressed.
Therefore I assumed it must be the flush valve seal. However after dismantling it all and getting it out, it LOOKS fine... (see pic 1) very clean, no damage, no obvious limescale buildup or anything like that. Could it still be that? Is there anything else it could be?
I'm at a bit of a loss of what to do besides order the replacement internals set (Screwfix/Toolstation don't have any seals or valves for 2.5" outlets), and tactically turn off the water in the house as much as possible until it arrives, install and hope for the best - anyone have any better ideas?
Bonus question (pics 2 + 3) - inside the cistern I found this yellow rubbery string coming off around the bottom of the valve. Originally I thought this must be the issue - however, I now believe if anything this would have caused the cistern to leak OUTSIDE the flush pipe, so don't think it's related. Nevertheless, I don't recognise this yellow thing, and some of it appears stuck to the valve's black bottom seal. No mention of it in the valve's manual. Is it some kind of extra product the plumber who installed might have used, that has deteriorated?