Grohe 27.05.44 Flush Valve - constant leaking into bowl

[YMF]

I am trying to fix a Grohe cistern flush valve. The code on the item is 27.05.44 4

After flushing, water is dischared and the tank is empty. When the tank is filling up with water, there is no leak into the toilet bowl. However, when the water level rises, to say 1 inch, water starts leaking into the bowl - so much so that the tank never fills up beyond the 1 inch level. .

I then experimented by pouring water into the tank. When enough water is poured in, the valve vibrates for a bit, then the leakage stops! And the tank fills up!

Can anyone please tell me whats wrong and if it can be fixed? Or do I need to replace parts of it or the whole thing. If I need to replacements, when can I find them!

Thanks very much for your help

 

[opps]

I am not a plumber...

I suspect that it might be a faulty washer at the very bottom.

My concealed cistern kept letting water run in the pan. I replaced the washer (a spare was conveniently left on the reverse of the flush pate).

Grohe Adagio Single Flush Toilet Cistern Flush Valve Discharge Piston & Base Sealing Washer 43544000

If your Grohe Adagio flush valve won't seal properly and is constantly passing water into the toilet pan but there is no sign of an inlet valve failure, it could very well be that the base sealing washer and discharge piston need to be changed. Over time as the flush valve is opened and closed...

www.toiletspareparts.com

Hopefully, a proper plumber will be along soon.

 

[Rodders53]

Not a professional plumber, either

That reference number finds https://www.fixthebog.uk/grohe-27-0...-model-42137-grohe-43544000-discharge-piston/ and from that Grohe number https://www.grohe.co.uk/en_gb/others-sealing-washer-43808000.html is the likely culprit for being worn/stiff/not sealing.

Search for the original install instructions as it may help with dis-assembly etc,.,.

This is the same as @opps has posted... but the washer alone is cheaper. Use some silicone grease lubricant. A small tube will last ages and has other uses. (Mine is RS branded and from the 80s in all likelihood).

 

[YMF]

Thank you opps and Rodders53 for your very useful responses. I had a look at the washer and it seems decent. As there is no leakage initially when the tank fills up, and the leak only happens after an inch of water, it seems to imply that the washer may not be an issue.

I then saw this clip on replacing part of the valve:

I pulled out the "piston assembly", cleaned it limescale remover, put it back in. And it worked! Not sure what I did right but its not leaking anymore. Thanks