I have a Triton Thermostatic concentric mixer shower fitting fed directly from my combi boiler. The flow control has become very stiff to open and close, probably due to limescale build up. If I take the flow control off, will I be able to increase the movement of it, or is the limescale in the main body of the fitting?
If it is caused by limescale then the limescale will be in the main waterways/body of the shower. I would strip the shower and clean all components, you may want to buy a service kit for the shower as you may need to renew O rings etc.