Pump runs 5 minutes and stops

the banging is the water boiling/overheating Check the pump is working by undoing the large screw on the front of pump and gently putting a soft stick into the space behind to check that the rotor/impellor is turning. take care to catch the water which drips from the screw hole

pump is producing pressure so it is ok
loosing pressure indicate pipes leaking or non return valve leaking

5 years is about the lifespan for tankless.
You might have shorted element. That would explain cooler water and tripping reset.
Test element: power is off, disconnect wires from element; ohms = voltage squared divided by watt rating of element
http://waterheatertimer.org/How-to-test-water-heater-element.html

Call service technician./ Call Bosch
http://waterheatertimer.org/pdf/Bosch-AE115-AE125_manual.pdf

Gene

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

HI Lawrence did you check to see if you have the right power going
to the unit

You need a 5 gallon bucket and a small sump pump that connects to a garden hose. The hose connects to the inlet of the water heater and and then run a second hose from the hot water outlet into the bucket. Pour in about a gallon of white distilled vinegar. Turn the pump on and let the vinegar run through the heater for 15 minutes. Reverse the hoses and run another 15 minutes. reconnect the heater and test the water flow. You may need to repeat these steps several times to remove enough debris and buildup.
Installing a water softener treatment system will prevent the buildup from occurring so fast, if ever again.

In order to clean the unit you need to connect a small sump pump to the cold inlet, and run a hose from the hot side into the same bucket. Pour about a gallon a white distilled vinegar in the bucket, and turn the pump on. Let the solution run through the unit for about 15 minutes, then reverse the hose connections and run the pump for another 15 minutes. Reconnect the water supply and outlet. Turn the water on in the bathtub first on the hot side and let ir run for a few minutes before turning the power back on to the heater. While the water is still running turn the power back on and reset the thermostat. If you get a lot of debris in the bucket, you may need to consider installing a water-softener to prevent scaling.

This is probably just the plug that is used to prime the pump if it looses it's prime, but I can't be positive since your description is a bit vague. I suppose that if you thought it adjusted something that you would be reluctant to just tighten it. Go ahead and tighten it. If it still leaks, then do the following:
Get some teflon tape (ask for it in the plumbing section at home improvement store or hardware store - $2 or less) Get a helper (a child will do). Turn off the power to the pump. Turn on the water at the kitchen sink until it stops running, then turn it off again. Now remove the leaking screw. Some water will come rushing out, but have your helper push his/her thumb over the hole (don't put a small finger IN the hole). Wrap the teflon tape around the screw in a clockwise direction as viewed from the bottom of the screw. Wrap about 5 layers, nice and snug. Don't leave a loose end that will dangle from the bottom of the screw. Put the screw back in the hole, nice and tight. Good luck, Al K

Hi,
The short answer is no.
You will not get any flow and wreck the pump.
Go to a Home Depot, Lowe's or Plumbing Supply House and get a 100' roll of black Poly Pipe and roll that out over the ground. The check also has to be at the end of the pipe and the pipe shoud slop away from the pump if possible. This will make it much easier to prime the pump. Air will cause the pump to lose it's prime so you want to get all of th air possible out of the pipe before starting the pump.

I hope that this will help you to solve your problem!

Thanks for using Fixya!!

Heatman101

I think the dip tube in your water heater has failed, this is a plastic tube that goes in the cold side of your tank and forces incoming cold water to the bottom of the tank allowing hot water out at the top. When this tube deteiorates the incoming cold water mixes at the top of the tank causing the problem you have. the dip tube runs about 5 bucks but takes someone with pluming skills to install.

Some circulation pumps have a 3 phase mixing valve (cold,warm,hot) to regulate the water pressure in the building; no way to know unless you trace the plumbing. Basically, the hot water temperature could be lost because the circ-pump is cooling it with the cold water supplied to it. This is used to balance the pressure (aka Pressure Balancing Circ-Pump), so heater is really working overtime to heat the water. If the pump has two in and one out that's more than likely your problem; but you should consult a "old-school" plumber in your area.