I have a Toto toilet that has a slow leek (it keeps running after it's full but goes down the drain - ie not flooding my bathroom). We replace the valve piece and went to turn the water back on and it started banging. Is this a preasure problem or something else and is it an easy fix?
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Check water pressure, cheap gauges available at big box stores, should be about 45-65lbs. Water hammer is commen with any appliance that has quick closing valves. There is usually and anti-hammer device where the water enters the house. This is often just a piece of pipe about 3' long with a cap on it. That is supposed to trap air and acts as a shock absorber. If that gets water logged, air dissolves into the water over time, it stops working. You need to drain down the system to let air back into that pipe, or add smaller anti-hammer devices at each appliance.
The toilet leaking is a separate issue. If it is just leaking down, the flapper valve is the usual culprit. If it is running into the tank overflow pipe, the water level needs to be adjusted to below that pipe. Both waste water, fix it.