Geberit Type 212 flush valve for Sigma, Delta and Omega concealed cisterns 245.895.00.1 Flush Plate With this Geberit flush valve's

With this Geberit flush valve's design you need not worry about removing the entire cistern to service the valve in future

High Performance -  flow rate up to 32 L/min

You can test if it's the bellows washer yourself with a simple method

Diameter: 62mm

it could very well be an issue with the button instead

Geberit Type 212 flush valve for Sigma, Delta and Omega concealed cisterns 245.895.00.1 Flush Plate With this Geberit flush valve'sGeberit Type 212 flush valve, complete replacement including base cradle. Valve also direct replacement for Geberit 241. 859. 00. 1 Authentic Geberit Spare Part Suitable for Sigma, Delta and Omega flushing plates, see fitting instructions Adjustable from 4 to 7 Litre flush Easy installation, no plumber required Fitting Instructions