No hot water

Usually, Breaker tripping indicates a hard short ... probably the heating element is shorted and needs replacement. Possible bad C/B but don't think so.
Good Luck! handy Henry.

If you need further help, I’m available over the phone at https://www.6ya.com/expert/henry_239f63a136de60f0

With on board thermostat...it's adjustable

It's scaled
Do you have a softener? Water must be 15 GRS/PPM or less in iron and calcium. Hot spots in unit are boiling water and are causing the noises.
Descale and flush unit following Rinnai Specs and check water hardness for compliance with Rinnai standards because too hard an inlet water will VOID the Heat Exchanger Warranty (10 year).

Has water heater been cleaned?

Check for lyme buildup in the pipes also check for a stuck water shutoff valve.

Good luck,

Marty

check this out.....
https://www.youtube.com/watch?v=eMeq-fRH-wE

These units need water flow/pressure to work. If you use a mixer to get the right temperature as soon as you try to increase cold to make the water colder you unfortunately reduce the hot flow. Fairly complicated fault to explain, all continuous flow units have the same flaw. Solution is to try and increase flow and the best way is to take any water filters or restrictors out of your tapware. Most taps have the located in the end of the spout. Unscrew the end and remove any restrictors. Shower roses are a bit more tricky to find. This fixes 99% of these problems.

check to see if you have a blocked line on the hot water side

curios to find out if you had any help on this subjuct at all?

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.