Broken or damaged dip tube allowing cold and hot water to mix in the tank.
Faulty plumbing installation has crossed cold and hot water connections
Gas supply or control problems
Make sure the hot water system is not being overtaxed by hot water supply demands. The hot water system should have 75% of its capacity as hot water (e.g., a 40 gallon WH should be used for a demand of 30 gallons).
Undo the cold-water inlet and pipe nipple and remove dip tube. Check the condition and replace if required.
Check for crossed connection by turning off the water supply to the hot water system. Open a hot water faucet. If there is water flow, then there is a crossed connection somewhere. Check for a hot water line connected to a cold-water connection on the water heater or appliances such as washer, dishwasher, faucet or shower valves.
Check for a proper flame from the burner. A natural gas flame should be bright blue with the tip of the flame having just a tinge of yellow. A propane flame should have a bluish green flame with a tinge of yellow at the tip.
Rust Colored Water
Corrosion occurring inside glass lined tank
Sacrificial anode rod is failing (anode rods dissolve slowly to prevent rusting in the tank)
Replace the sacrificial anode rod with magnesium anode rod. Anode rods are available from a plumbing supply house.
Rotten Egg Smell
Bacteria in the tank sediment fed from hydrogen gas created from decay of sacrificial anode.
Flush the hot water system using a hydrogen peroxide solution of 2 pints 3% peroxide to 40 gallons of water, treat tank and run some of the solution into water lines.
Let peroxide solution set in the tank and pipes for 2 hours. The Solution is not toxic and requires no rinsing.
If the problem persists, replace the anode with a zinc-alloy anode.
If the problem still remains, replace the hot water system with a plastic lined tank type.
Low Rumbling or Popping Noise
Noise heard is the sound of boiling water. Excessive buildup of sediment in bottom of the tank is causing overheating of the tank bottom and boiling of water to occur.
A faulty T&P (temperature and pressure) relief valve
The T&P valve leaks due to excessive pressure, overheating or is stuck
A leak from overhead or nearby plumbing connection
A leaking water tank (corrosion likely)
Place the bucket under overflow pipe. Open and flush T&P valve clear of debris. If the leak remains from the valve, replace the valve.
Reduce the thermostat setting to prevent tank overheating and opening T&P relief valve.
Inspect bottom of the tank by looking through the combustion chamber. If water marks or heavy rusting is noticed or if water is noticed setting in the combustion chamber bottom, then the water heater needs to be replaced.