Once in a while after burner has been on and shower has been on for a while, the burner shuts down and pilot flutters, then pilot comes back on good but no burner .eventualy burner comes back on. if i turn water off and then back on burner will come on.

Tankless?... call service technician

Tank? clean arrestor screen, replace gas valve thermostat
http://waterheatertimer.org/How-to-troubleshoot-gas-water-heater.html

http://waterheatertimer.org/How-to-troubleshoot-gas-water-heater.html#intellivent

Gene

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

What are you expecting to happen?

I assume the water heater and water inside it is cold (otherwise you would not be lighting it). You light the pilot. The main burner comes on and the pilot lights it. The main burner should stay on until the tank is hot, When the tank gets hot the main burner should shut off but the pilot stay on. If you draw hot water, cold water will run in and cool the tank. If yu do nothing the tank will eventually just cools off. then the main burner should come back on to reheat the tank.

Suspect the thermocouple that senses that the pilot is lit. This device prevents the gas burner from coming on when if the pilot goes out, but if it's defective could cause the burner to shut down even when there is a pilot flame. Also check the position of the thermocouple in relation to the pilot flame. The tip of the thermocouple should be right in the middle pilot flame.

I looked up this unit for you and found out it is a hot water system. She needs to get to the main gas valve to light the pilot. This unit has what is called a thermocouple on it that keeps the pilot on, even when the boiler shuts down. Its just a matter of lighting the pilot light. There should be a metal plate with the directions on it at the gas valve to lite it. You will have a knob, more then likely red or black in color on top of the valve. It will say on, off, and pilot. It should be in the on position now. Turn it to pilot. Have some matches with you and a flashlight if you can. You will need to look back into the burner area to where your pilot light will be. The thermocouple is a copper colored tubing that runs right back to the pilot, as it has to get hot from the pilot flame to work. To start, depending on how far back you have to reach with the match, you may need to use a piece of solid cardboard rolled up, a small piece to light it and reach in. Turn the knob to pilot. Now, push down on the knob and hold it down. This lets gas get back to the pilot, so you must keep it down and light it at the same time. Once it is lite, you have to hold it down for at least a minute. Slowly release it, very slow. The flame should then stay on. Once it is on, turn the gas knob to on. With the thermostat set to come on, it will fire up and heat the water. If the pilot will not stay lite after you hold it down for 1 minute, and keeps going out, the thermocouple will need to be replaced. It is the copper line that screws into the gas valve and goes back to the pilot. You can get them at any hardware store for around $6.00. Maybe you can help her install it. It is very simple to do. I believe the pilot just blew out and she will need to light it. Just follow what I have told you, and she will get it lite. Good Luck to you.

Ok the way this system works is from a pressure and flow switch. The pressure switch picks up the slight drop in pressure when the hot side water is turned on then turns on the burner. The flow switch measures the amount of water flowing and adjusts the size of the burner to the amount of water flow. So a couple different things might be happening. The flow switch might be sticking causing the water heater to throttle down the burner but not off when the water flow is off. Or the gas control valve might be by-passing gas when off causing the burner to stay on even when the demand is off. Run the hot water on high demand then turn the water off. If the burner is still on try banging on the water heater with your hand and see if the burner shuts off completely. If it does the gas control valve might be by-passing. You would also need to check and see if the pressure/flow switch is giving any voltage signal changes when the water flow is off. These tankless water heaters are more comlplicated to work on than a standard water heater and you may need a professional's help...good luck

Often, this is the result of a restriction of exhaust gases. This type of hot water heater must be adequately vented, (per installation specs). I found this out after taking a number of cold showers. :^( Two years later, and still counting, no more problems. :^)

the pilot is getting too much air and is an indicaiot of dirty or air/ fuel ratio imbalance. The pilot is wimpy and the thermocoupler has alot to do with the gas . Make sure your thermocoupler is on the tip of the flame. You may end up replacing it. because it is showing signs of eminnt failure. When it fals your curners won't fire up. Good luck.

One of the proper ways to light a gas water heater, is to turn the black knob to Pilot, put a match to the end of the pilot light, while holding the match there, push the red reset button down and hold the match & the reset button down for one full minute. Then, release the reset button and turn the black knob to On. This should keep the pilot light on.

Sounds like the gas valve has failed. The gas valve can be replaced. It will unscrew out of the tank. Shut the water supply to the tank off and get the new gas ready to screw in. Take out the old and screw in the new, you will onlt lose about a cup or two of water if you are quick enough. Otherwise drain the tank down if you must. If you are going to replace the gas valve I would also replace the thermocoupler.

it also sounds as though the pilot injector could be blocked so when the boiler comes on it extinguishes the pilot & then when the burner goes off boiler shuts down, or also the pilot rate maynot be set right, so when the main burner kicks in it robs the pilot of the gas it requires.
It could be that, or there is lack of ventilation for the boiler, so you get flame lift off when the boiler fires?