Water heater supplies about a pint of hot water than turns cold?? what is th eproblem

did water stop if not problem can be with install --or faulty valve https://www.reddit.com/r/Plumbing/comments/lzde4a/rheem_marathon_install_vacuum_relief_valve/

It sounds like there is too much pressure in the hot water pipes. You can try adjusting the pressure. Do it a little at a time to see how much hot water is coming out. The only other thing I can think of is that there is a large delay between the switch and the water flow. meaning you will need to stop the water a while before you actually want the water to stop flowing.

Elisa Jed ' http://www.mccreeryhvac.com

may have a screwed up washer seal on the hot side..it will stop the flow to a degree and allow more cold water in..calls for dismantling the entire control or replacing it..

Centre tap of the rinnai will turn off hot water supply only.
Easiest way is to turn off your mains water supply. This will isolate both hot and cold, no need to turn off anything else

The inlet line to the water heater goes to the bottom of the water heater to prevent the cold incoming water from mixing with the heated water at the top. The tube going to the bottom can come loose.

Turn the water off and relieve the pressure by opening a faucet and remove the fitting where the water enters the heater. You can see if the pipe is still connected.

Not sure but check the inlet water at the heater, the filter may be clog up a little that restrict the flow. Did u use the heater at all during the winter? If not, the heat exchanger may be clogged with built up in there. U need to descale it. Good luck. Chinhcu

In city water or well water system ... the cold water flows from the tank (or meter) toward the hot water heater. The cold water splits in two (so to speak) at the heater with one part going on to the house to supply all cold water needs while the other part goes into the water heater to be heated. On the other side of the hot water heater, there is a system that paralles the cold water system to supply the hot water needs of your home.

I hope this answers your question.

It could be back flowing into the hot water heater tank which is not full because of the leak. Even though the valve is closed on the cold water entry side, there is probably no valve on the exit side. That is how it is returning to the tank.

basically the principle of the heater is water flows into a internal tank and is heated by an element. You open a hot tap and the mains cold water forces the hot out and replaces it inside the heater.As you have a flow problem i can only suggest you may have some kind of restriction or blockage in the cold water supply at the water heater or from the hot supply from the heater.If you live in an area where lime content is high then this can calcify when heated.If you can, isolate the water supply and electrical supply and check the pipework for blockage.Also investigate your hot tap as this may be the fault. Good Luck

I wonder if you have this problem below caused by a drop in water pressure from someone flushing a toilet or a washing machine. I would call the company to remedy this issue.

17. What is a cold water sandwich effect? The term “cold water sandwich effect” is a term that is used to describe the introduction of cold water into the hot water supply line during frequent on/off operation of an instantaneous water heater. The cold water sandwich effect, when present, appears as a momentary drop in hot water temperature as it is discharged from a hot water supply outlet (i.e. shower, tub, or faucet). This phenomenon is present in the operation of all instantaneous, tankless style, water heaters, but is minimized with the high tech design of Rinnai water heaters.
The technology built into the Rinnai water heaters is designed to minimize the cold water sandwich effect. Rinnai water heaters are microprocessor controlled and when water flow through them ceases, they remain in a “ready to fire state” for approximately 1 minute. If water flow through a Rinnai water heater begins within the first minute following water flow stoppage, the water heater will fire back up within 1 to 2 seconds. This minimizes the cold water sandwich effect that would otherwise be experienced with a low tech tankless water heater. It should be noted that the cold water sandwich effect cannot be removed completely from tankless style water heaters. The safety standards developed to insure the safe operation of water heaters require a delay in the ignition sequence of all gas water heaters.
While the cold water sandwich effect cannot be completely eliminated from standard plumbing systems, it can be eliminated from plumbing systems that have a supply and return hot water circulating system. Rinnai has developed 2 methods to eliminate the cold water sandwich effect in residential hot water circulating systems.
The first (and preferred) method to remove the cold water sandwich from circulating systems utilizes a small electric tank water heater (powered up) that is used with a dual purpose. The small water heater acts as a mixing tank to eliminate the cold water sandwich effect from the Rinnai water heater and it uses its electric heating element to offset the heat losses from the hot water circulating system.
The second method to remove the cold water sandwich from circulating systems utilizes a small 2 to 6 gallon storage tank installed on the hot water outlet of the Rinnai water heater. This tank acts as a mixing tank to blend the cold water sandwich with hot water and eliminating its effect at fixtures.