Published in hometips.com, Water Heater Troubleshooting & Repairs
An undersized water heater is usually the culprit if it seems like you never have enough hot water in your home. If the problem is chronic—or if you’ve increased your needs for hot water by installing a new soaking tub or high-flow shower head—you’ll probably need to get a new, larger water heater. Be sure to look into tankless water heater because, with this type, you never run out of hot water.
On the other hand, if you’ve had enough hot water in the past but your water heater suddenly seems to supply less hot water, first check the dial on the water heater, as discussed above. Also make sure it isn’t leaking. If neither of these issues are the problem, flush the water heater tank to be sure mineral deposits are not reducing the heater’s efficiency. To do this, please see How to Flush or Drain a Water Heater.
Attach a hose to the water heater’s drain valve and empty the tank.
This is also a good time to test that the temperature-pressure relief valve, which keeps pressure from building up too much in the boiler, is in proper working order. Lift or lower its handle. Water should drain from the overflow pipe. If it doesn’t work, see How to Replace a Water Heater TP Relief Valve.
If these measures don’t do the job, the dip tube that supplies cold water to the tank may be broken or cracked. This plastic tube is supposed to direct cold water to the bottom of the water heater tank, but, if it breaks or splits, cold water pours in at the top of the tank and mixes with the hot water that is on its way to the hot water pipes.
Either have the dip tube replaced by a water heater repair pro, or, if the water heater is out of warranty and showing other signs of age, consider replacing it.