Grohe Adagio - leaking into cistern, discharge piston already replaced

[PeterT]

Hi - I'm looking for some guidance with a problem with the Grohe Adagio discharge piston/seal which leaks part way through refilling. I've seen this raised before but there didn't seem to be a resolution.

We have a couple of Grohe Adagio concealed cisterns, both 16 years old. With one I have a leak problem from the cistern to the toilet pan. Its not related to the water inlet which is new and stops filling at 2cm below the top of the overflow entry into the flush mechanism.

With the flush mechanism I've removed it from the cistern, descaled it, the cistern & the cistern outlet pipe and replaced the discharge piston & base sealing washer using Grohe part 43544000.

What happens now is that when refilling, the water level gets up to about 50mm deep (1/2 way up the vertical cylindrical part of the mechanism) at which point water starts to leak out of the cistern into the toilet pan. Normally the volume leaking out matches the incoming from the feed and so that cistern doesn't fill any further.

When I then add water manually with a jug to take the level up another 20-30mm the water leak into the toilet pan ceases and the cistern continues to fill as it should.

What can I do to fix this and make the toilet useable again?

 

[Ben-gee]

Weak spring in the flush valve- replace the whole valve and keep your discharge piston as a spare.

Assuming you have seated the prong of the bellows correctly on the edge of the flush valve?

 

[PeterT]

Weak spring in the flush valve- replace the whole valve and keep your discharge piston as a spare.

Assuming you have seated the prong of the bellows correctly on the edge of the flush valve?

Thanks - I've reseated the bellows and problem seems to have gone away