Buttons on our concealed dual flush cistern have stuck in, water constantly running into pan?

Help and videos in the link. Not so easy when they are 'concealed'.

https://www.google.com/search?q=Tavistock+vortex+concealed+cistern+replace+flush+valve

..

the amount of water in a pan is set by the height of the bend at the back
If you are asking how to get more water to flush the pan, raise the water level in the cistern by adjusting the water control height in the cistern

The flush control panel normally comes off. You can then hopefully see inside. You won't be able to see much though as the cistern will be in the way...

Places to look for leaks are:
Soil pipe to pan
Cistern to flush pipe
Flush pipe to pan
Cistern overflow.

Grohe Flush Valve Replacement

That would be a leaking flapper valve. They are inexpensive and easy to install. Good luck

I’m happy to help further over the phone at https://www.6ya.com/expert/robert_24775b73ca70da93

hey, since it is new, I assume a small stone or left-over is stuck where the seal is, You need to disassemble the valve, clean it and re assemble. Look at this guide that might help you. though it is not the exact model, principle is the same.
Have fun
Avi Grohe GD2 flush system concealed cistern repair fix and disassembly...

check the donut seal which seals the cistern to the pan, they perish and leak when the toilet is flushed, water runs down back of pan to floor you can check this by drying/wiping with tissue back of pan and flushing you will see if any moisture is running down there by wiping again with tissue and seeing if it is damp.

well, yes... but apart from providing you with a forum in which to vent your frustration I'm not sure how you think we might help. I have the same problem with a dual flush cistern, but in my case I know that the root of the problem lies in the fact that the soil pipe leading from the bowl has insufficient fall (because the previous owner of my house moved the toilet further from the down pipe). Maybe something like this is contributing to your problem too?

hey,
Check your button/s panel, check that the hoses are connected firmly.
Disconnect the hose and blow air through it, does it work now?
If it works ok, you need a new buttons panel. (or fix it).
If problem remains, you need to disassemble the pneumatic valve and check / clean/ repair it.
Look at this guide that might help you. though it is not the exact model, principle is the same.
Have fun
Avi

Grohe GD2 flush system concealed cistern repair fix and disassembly...

No I'm sorry they do not. You might try plumbing supply house in your area.