Hi - after about 10 years use one of the valves (on/off flow) ceased up. Tried getting a replacement but struggled to find an exact matching one... Found your video and tried flushing the part in timescale remover - wow! It worked a treat. Have it several washes in the remover and slowly eased it back and forth. Left it in the wash with the valve open, then shut, then half way, and worked it both ways between soaks. After several washes and wiping away the loosened timescale the valve is now back in and working as good as new. Thanks for the video - saved us loads of hassle... 👍

How much did you mix of that to clean the valve?

All round terrible shower valve