Fixing a faulty valve with This Old House plumbing and heating expert Richard Trethewey. (See below for a shopping list and tools.) SUBSCRIBE to This Old House: http://bit.ly/SubscribeThisOldHouse Shopping List for Replacing a Shower Mixing Valve: - new shower valve - plumber's grease, for lubricating O-rings Tools for Replacing a Shower Mixing Valve: - utility…