Our Hydrojet gas water heater stopped producing hot water all of a sudden. I was wondering what kind of things we can do to get it started again.

It’s obviously leaking. If Liner is leaking replace heater. If piping is leaking, replace leaking pipe.

Unless you are using a tankless hot water heater, there is a limited amount of hot water available in the tank. Electric and gas water tanks need time to recover after use, and if you are using heavily, it can exhaust the available supply. That said, there are a couple reasons why you may have less hot water than seems normal. In both electric and gas water heaters, silt can form in the bottom of the tank. This will build up over time and displace water. It also reduces the heating efficiency of gas units. There is a drain valve on the bottom of water heater tanks to allow for purging of this silt periodically, but few ever do it. You could also have, in the case of an electric hot water heater, a bad element or thermostat. Most electric heaters have an upper and lower element and thermostat. If one fails the other will still work, but the water takes longer to get hot and will deplete faster.

What type heater:

1) Electric: press reset button located under front cover, check circuit breaker:
http://waterheatertimer.org/How-to-troubleshoot-electric-problems-with-water-heater.html

2) Gas: clean air intake, call for service:
http://waterheatertimer.org/How-to-troubleshoot-gas-water-heater.html

3) Tankless. Throw it away and install tank-type.
http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html
http://waterheatertimer.org/How-to-install-gas-water-heater.html

4) Add a comment with more information about your heater.

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

1) Clean air intake, and do required yearly maintenance.
http://waterheatertimer.org/How-to-troubleshoot-gas-water-heater.html#intellivent
http://waterheatertimer.org/How-to-replace-thermocouple.html

2) Gas control valve thermostat could be going bad, causing disruption of gas to pilot, and uneven heating of water.
http://waterheatertimer.org/pdf/How-to-replace-water-heater-gas-valve.pdf

3) Without knowing brand and model number that shows on label on side of tank, it is difficult to add specifics.

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

here's what Bradford White lists....
Burner Will Not Ignite
REASON REMEDY Excess primary air Adjust air shutter to reduce air supply -- if supplied No gas Check with utility Dirt in main burner orifice Clean orifice -- check for source of dirt and eliminate Dirt in gas lines Notify utility -- install dirt trap in gas line Venturi clogged Clean -- check for source of trouble and correct Pilot line clogged Clean -- check for source of trouble and correct Main burner line clogged Clean -- check for source of trouble and correct Defective thermocouple lead Replace with new thermocouple lead Defective thermostat Replace Defective magnetic valve Replace entire control Thermostat set too low Turn temperature knob to desired temperature Heater installed in confined space Provide ventilation by use of louvers in wall or door time for a service tech.

The slightly warm water makes me think of a thermostat problem. The fact that the heater is 10 years old I wonder how hard your water is. Calcium build up kills water heaters. But the yellow flame you mention could be the results of dirty orfices. May want to have a Pro look at that.

Have you try to reset the power to the heater?Then turn the hot water facuet on to see if it will start up.

someone has messed with the differential setting - so the water heats to correct temp but cools too low before coming on. get book -easy fix