Want to change water faucets

follow this steps and fix it. God bless you
Drain a tank:

1. Shut off power at the electrical service panel and post a sign warning others not to turn it on.
2. Close the cold-water supply valve and open a hot-water faucet somewhere in the house (to speed draining).
3. Attach a garden hose to the drain valve and run it outside the house.
4. Open the drain valve and allow all water to drain out.
5. To refill the tank, close the drain valve tightly and open the cold-water supply valve. Also open a nearby hot-water faucet. When a steady stream of water flows from that faucet, the tank is full and the faucet can be closed.
6. Once the tank is full, turn the electrical power back on

Test and replace a heating element:

1. Turn off power at the electrical service panel and post a sign warning others not to turn it on.
   
2. Remove the access panel on the electric water heater.
   
3. Disconnect one of the element wires and set a multimeter to RX1000 (resistance times 1,000). Touch one probe to an element mounting bolt and the other to each element terminal screw, in turn. If the tester displays anything but infinity ( open circuit), replace the element.
   
4. If necessary, set the multimeter to RX1 and touch the probes to the terminal screws. If there is any resistance reading at all ( closed circuit), then the element is good. If not, replace it. Both upper and lower elements are tested in the same manner.
   
5. To remove the element, first drain the heater.
   
6. Disconnect the remaining element wire. Remove the mounting bolts holding the element in place. Remove the element.
   
7. Replace the heating element with one of the same model, shape, and rating. Make sure you also replace any installation gaskets.
   

Test and replace a high-limit cutoff:

1. Disconnect power to the heater at the electrical service panel and post a sign warning others not to turn it on.
2. Remove the upper access panel and push the reset button.
3. Replace the access panel and turn the power back on. If the water is hot, the reset was the problem. If not, you'll need to turn the power off again and reopen the access panel.
4. Use a multimeter to test the cutoff terminals for continuity. If faulty, replace with an exact replacement part.

follow this steps and fix it. God bless you
Drain a tank:

1. Shut off power at the electric panel and post a sign warning others not to turn it on.
2. Close the cold-water supply valve and open a hot-water faucet somewhere in the house (to speed draining).
3. Attach a garden hose to the drain valve and run it outside the house.
4. Open the drain valve and allow all water to drain out.
5. To refill the tank, close the drain valve tightly and open the cold-water supply valve. Also open a nearby hot-water faucet. When a steady stream of water flows from that faucet, the tank is full and the faucet can be closed.
6. Once the tank is full, turn the electrical power back on.

Test and replace a relief valve:

1. Lift the spring lever on the valve to fill a small cup. Check the cup for sediment.
2. If no water spurts out, or if water continues to drip after the valve is released, replace the valve.
3. Cut power at the electric panel and post a sign warning others not to turn it on. Close the cold-water supply valve.
4. Drain a few gallons of water from the tank.
5. Unscrew and remove the discharge pipe if used.
6. Loosen the relief valve with a pipe wrench, then remove the valve by hand.
7. Apply pipe tape to the threads of the replacement valve and screw it into the tank by hand. Tighten it with a pipe wrench. Screw the discharge pipe (if any) into the valve outlet.
8. Refill the water heater and restore electrical power.

Single-handle faucet cartridge that leaks can cause tankless not to function. Check for crossover or cross connection:
http://waterheatertimer.org/Crossover.html
Cut losses from owning tankless computer that heats water. Go to Lowes and buy new tank-type gas water heater for $390 and have hot water right quick with less maintenance and own a product that homeowner can repair themselves.
http://waterheatertimer.org/How-to-install-gas-water-heater.html
Otherwise call service technician who is qualified to work on tankless computer.
Gene
n

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

Bad PC board.
Bad sensor.
Don't buy a tankless because the problems can be endless.

Before blaming the tankless however.
Perform the yearly required maintenance on burner
Delime the unit.
http://waterheatertimer.org/pdf/Bosch_Descaling-heat-exchanger.pdf

Remove and clean aerators, replace low-flow shower heads with large water-wasting shower heads.

IMPORTANT check all your single-handle faucets for crossover.
Water getting cool after 15 minutes could be bad cartridge on another faucet.
http://waterheatertimer.org/Crossover.html
http://waterheatertimer.org/pdf/No-Error-Code.pdf

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

clean filter on the cold side coming in and clean or replace the aerator at the sink, rinnai works on water flow, common problem if your water hardness to high or if you have iron in your water

Your circulator provides the draw necessary to fire the heater. You are defeating the purpose of this kind of heater by circulating the water. Add a second heater to fix this engineering fault.

You need to first make sure is the tankless who do the “up and down”! . If the problem manifest on more then one faucet then the problem is the unit. Have a thermometer (we use a infrared gun wich we train on Hot water pipe !) and see if actually the unit is the culprit.
If the problem is only on one shower It is possible also to be a “antyscalding valve” If the trigger valve on your shower is being adjusted too low then it trigger a splash of cold water now and then on regulate intervals. Try to adjust the temperature lower at the unit (say 110F ) and see if the problem change. If it does, then the problem is for sure in the faucet. If it does not change , then you have a problem with the water flow sensor . It is simply getting stuck. Bad bearing or even a piece of Teflon tape. I believe you will need a certified technician for that so no issues with your warranty will appear.

The gas pipe size that heater has to 3/4 pipe size.If you got anything any smaller than that is won't give enough gas.Check the gas psi at the heater.If it's bottle gas you should 11 psi.and natural gasline you need 5psi.

it comes on when the pressure changes so when you open another faucet it changes the pressure and makes it come on,, check your pressure regulator valve on the main line comming into the house it has a screw in the center, if you have a pressue gage put it on either the water heater drain or out side hose bib , check the pressure when turning water on and off if it changes more then 5 lbs you need to change your prv valve. pressure regulator valve,

Its A Possibility The Left Over Water In The Hot Is Frozen. If Your Line Is Exposed Outside Somewhere It Can Easily Freeze Up. Turn On The Hot Water Everywhere In The House And If Accessible Check The Lines To See Where The Warmth Ends. You Can Leave One Off Over Night In Hopes That It Will Eventually Defrost.