Change o ring - Bosch PowerStar AE125 AE125 Whole House Electric Tankless Water Heater...

no info generic answer --check thermocouple --and safety switches

It sounds like the cartridge is not properly seated against the O ring. I am not familiar with this exact model but remove the filter, check and be sure the o rings are ok and re install the filter.

first check to see if the thermocouple is close enough to the pilot. if it is and won't light the ring, replace the thermocouple.

No, its correct. Its just labeled incorrectly in the manual. The Bushing should be pushed up all the way(use dish soap to lubricate that oring) and the clip installs on the bottom of the bushing.

What do you mean ringing? Is it gas or electric? tankless? when does it ring? when its hot? when its being used? when it shuts off? Need more info to help you.

It sounds like you have an electric water heater and it kinda sings in a high pitch? If so thats the element heating up and thats usually not a big problem. Some times it can be a sighn thats the tank needs to be flushed or the element going out. But time of year it just the water comming into the water heater is just a lot colder than in the summer time and the heater has to work harder to heat that colder water.

Use CLR from local hardware and pumice stone.
This will remove any problem and shine it right up.

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

I had the same problem. There is a 2 piece metal tank inside. The top and bottom of the tank are connected with screws & nuts, and there is a rubber o-ring between the two pieces. The grove for this o-ring is very shallow and it doesn't fit tightly, increasing the probability of misalignment during the assembly process. I was unable to fix the leak, IMHO the grove is too shallow and the o-ring is not thick enough. I decided it was poorly designed & trashed the unit.

You need to cut water supply to filter, you may want to put a bucket or something to catch water under it, then, press the button on filter to release pressure in filter. If you have a wrench for it, the wrench should slide up from bottom and engage ribs on side of filter. Turn counter clockwise to remove, sometimes you can do this by hand. You can also use a strap wrech, just don't break canister. You also want to try not to strain your pipes if they are not supported. Any way, you may have to figure a way to grip canister to twist off. You do not want to overtighten for this reason. After you change your element, make sure the o-ring in the lip inside of canister is in place. Twist back on, clockwise. Turn your water on and check for leaks.

If you were simply changing the filter, then I would pull the new cartridge back off and inspect the o-rings. It's possible that one got bunched on the install and is blocking the inlet/outlet of the water. Other wise if you had to turn off the water any where to change the filter, check the valve that the water runs through to see if it is turned on all the way.

you will have to shut your water main off to repair. Drain plug , you may need a new o-ring replace 0-ring and turn water main back on, remember to relieve the air pressure with the relief valve.