WC runs after flushing — identification of flush mechanism and repair

[Ulsinus]

My WC has just developed a problem.
It flushes OK but then the water keeps draining into the pan.
The cistern is a concealed/built-in one.
I lifted the cistern lid expecting to find a siphon but the arrangement is quite different.
I would find it really helpful if someone could identify:
1) the arrangement and manufacturer,
2) explain what the cause of the problem is, and finally
3) what I can do to remedy the situation.
Please see the attached images.
Thanking you in anticipation for your guidance and help.

 

[Riley]

Thinking grohe or geberit flush? You can pop the flush out and take it to a merchants. It could be scaled it could have a worn washer

 

[Ben-gee]

That is grohe dal, you will most likely need a new discharge piston 43544 000. Easy to change, it is at the base of the flush valve.

 

[townfanjon]

Grohe adagio ( probably wrong spelling )
Either , the inlet valve is letting the cistern over fill and its directed into the pan
Or as Ben above sugests if could be the drop valve letting buy .
One or the other , just refill and see where the water level is .... great cisterns!!

 

[Ulsinus]

Thank you both for your advice. Armed with your information I've found a guide on YouTube about replacing the 'plunger'. Couldn't have done this without your advice. Once again thank you.

 

[Ulsinus]

Thank you Townfanjon. The cistern is not overfilling. So it points to the drop valve or in newbie speak the plunger. Also for being more specific about the model — Grohe adagio

 

[Ulsinus]

I've tried 'popping the flush out' but can't do it. It seems to be firming held in place by a 'overhead gantry'. This seems very firmly fixed in place. I don't want to force anything in case I break something and end up in a real mess. Any advice?

 

[Ben-gee]

Have to take your brave pills I'm afraid! The gantry lifts off upwards, as you've discovered it can be quite stiff after several years and a bit of limescale.
If you can 'flex' the cistern a little to break free any scale, that can help. I have tapped upwards from below with a length of 2x1 batten in the past - keep it flat to the cradle to avoid uneven pressure which is more likely to break off a lug.
Don't worry too much - it is stronger than it looks (it is also available as a spare part if the worst should happen - I have never broken one yet though)

 

[Ulsinus]

Thanks Ben-gee. The fact that it can be removed is reassuring and that if things go wrong that a replacement part is available..