I live in a real hard water area and after about a year my shower head gets full of limescale. I remove it and put it into a box filled with white vinegar. I leave it overnight and this dissolves a lot of the limescale but when I refit the shower head there is a lot less hot water. The pressure is better but the temperature isn't as hot as previous. I have to whack it on full temp for it to start coming out properly. I thought the vinegar trick would solve all this. What am I doing wrong?