We have a water heater in the basement that whistles whenever it is either filling up or heating the water. It has been doing this for the past six weeks or so. What is the cause and how can I fix it ?
Gary

 

The only place that a water heater could normally be "whistling" from is the Temperature & Pressure relief valve near the top of the heater tank.

Temperature & Pressure Relief Valve
It could be due to pending failure of the T&P valve (or due to some other reason) making it "whistle".
Replace the T&P valve first to see if it stops.
Turn the gas or power OFF to the water heater.
Turn the cold water supply OFF to the water heater.
Open a nearby hot water faucet to relieve pressure.
If the T&P valve is on the side of the heater instead of out of the top, you also might want to attach a hose to the drain spigot at the bottom of the heater and drain it down a bit.
Wrap 2-3 flat turns of teflon tape clockwise only around the threads of the new T&P valve, and tighten it in.
Turn the cold water supply back on and let that nearby hot water faucet run until all of the air is out of the heater and hot water line, and you have a steady flow of water.
Then turn the gas or power back on.
Good Luck! Mike