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Constantly running toilet

My upstairs toilet is currently taking an incredibly long time to fill up, being quite noisy while it does. It also then constantly runs, causing a regular dripping sound. I also have a basin in the downstairs toilet which leaks when its used. Finally the release valve for my hot water cylinder apparently has a leak which drips onto my roof and causes corrosion. I would like to know my options for repairing this, but also for switching the cylinder from a low pressure one to a main pressure.