Look at the flame and see if it's burning blue or yellow.
And then see if it's burning all the time. If the flame is yellow and water heater does not make hot water, the thermostat may keep the flame going all the time and use up your gas.Poor flame color means you should clean the burner
or replace the burner. If water heater is exposed to trace amounts of some chemicals, like bleach or pool chemicals or wax, these chemicals get pulled into the burner and will shorten life of burner assembly and combustion chamber.If the flame is blue and the water is not hot
, then the thermostat is the best suspect. The thermostat is part of the gas valve. The gas valve has a copper tube that extends into the water and reads water temperature. If thermostat reads incorrect temp, then the gas valve needs to be replaced with gas valve from local plumbing supply of Lowes.If the flame is blue, and it runs all the time
, then your tank may have a layer of sediment between the flame and the water, and the sediment has caused water heater to become very inefficient.http://waterheatertimer.org/Clean-sediment-out-of-water-heater.html
Now to answer your question
You can turn up the thermostat dial located on front of tank.
Check your flame and how often burner comes on to determine where problem is.
You can buy a gas valve from Lowes for $65 or from plumbing supply and then replace >> you need a couple wrenches and pipe joint compound and about half a day.
You can clean the burner with wire brush and shop vac.
Remove chemicals from same room as water heater.
If the water heater has sediment build-up, then a new water heater is probably best choice.
You can do some things yourself. If the do-it-yourself steps don't work, then get a new water heater
, and you know more about maintaining a water heater because you worked on the old one. Save the new water heater manual. Read the manual because it has ordinary information that will save you money long-term.How to determine age of water heaterhttp://waterheatertimer.org/pdf/WaterHeaterSerialNumberDecoder.pdf