I've fitted a thermostatic bath/shower mixer in the bath and initially all works fine but after a few weeks the pressure drops. If I remove the shower body and let water flow out fully then reattach the body, all works fine again for a few weeks. The shower is connected to a gravity fed hot water system with mains cold water. The hot water is connected to the cylinder via the top of the tank. No surrey or essex flange has been used and no pump is installed. I'm thinking that an essex flange is needed to prevent any airlock?? Any thoughts? [/b]