042-VGCC and water flow, bathroom faucet, cold water and hot water by themselves have very low water flow, combined they have a nice flow

problem in the tap washer (expanded and blocking the water flow
blockage inn the connection where the shower head connects at the wall
hot water flow restrictor so that you will not get burnt by the hot water --test by turning on the cold water first and then opening the hot tap as well

Check for restrictions in the shutoff valve and the stem of the hot water side.

Check for crossover problem where cold water is getting into hot line and causing less flow on hot line that cuts off heater and reduces temp at faucet.
http://waterheatertimer.org/Crossover.html

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1) Guesses: Sounds like a bad single-handled faucet cartridge, or low water flow at faucet, or clogged water filter.
Replace faucet cartridge, clean the aerator, and/or clean sediment out of pipes below sink, and clean water filter at tankless unit each month.

2) For exact measure of problem:
Typical faucet can have 2 gallon per minute flow rate.
2 gpm flow rate means faucet fills 1 gallon container in 30 seconds. Test faucet using 1 gallon container and a cooking timer to get flow rate.
Clean aerator to improve flow rate. Compare kitchen flow rate with other faucets in home.
http://waterheatertimer.org/Low-hot-water-pressure.html

Most homes have 1/2" diameter pipe running to kitchen faucet.
100 feet of 1/2" diameter pipe holds 1.2 gallons of water. This assumes no sediment build-up inside pipes.
http://waterheatertimer.org/Water-heater-recirculation-system.html

Assuming only hot is turned on: If faucet is 100 feet away from water heater, and pipe diameter is unobstructed 1/2" diameter, and faucet has 2 gallon per minute water flow, then hot water should arrive in 36 seconds.
50 feet away, and hot water should arrive in 18 seconds.

If kitchen has single handled faucet, and the handle is raised in the middle, then equal amounts of hot and cold water are drawn at same time. This doubles amount of time for hot water to arrive.

If single handle faucet has a bad cartridge, then faucet can have crossover.
Crossover means that cold water can enter the faucet even if faucet is turned to hot.
Bad single-handled faucet cartridge can delay or stop the arrival of hot water.
http://waterheatertimer.org/Crossover.html

Tankless require maintenance including cleaning combustion parts yearly, de-lime heat exchanger frequently, and clean water filter each month.
http://waterheatertimer.org/pdf/Tankless-maintenance.pdf
http://waterheatertimer.org/pdf/Bosch_Overcoming_fluctuating_temps.pdf
http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html

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There is a minimum water flow required to operate your Bosch tank-less water heater. It is around .75 gallons a minute. There are three things you can do to help the flow.
1.Turning the temperature down will help increase the flow.
2. Installing higher flow aerators on your faucets.
3. Clean the Bosch tank less water heater.
You are not alone in having this issue. The most common problems are low flow faucet aerators and low flow shower heads.

chances are that you have a bad faucet that is drawing water from a cold water tap. You will need to have a helper turn on the hot water in that bathroom while you feel the pipes at the water heater and see if they are heating up. If they feel like there is no flow, the water is coming from somewhere and you will need to turn the shut-offs of at various sinks to target the problem faucet. If you find which cold water line is acting up, install a back-flow check valve so the water goes only one way, toward the faucet.

MOST LIKELY YOU HAVE A CLOG AT THE SEAT ON THE INSIDE OF THE FAUCET, TYPICALLY SAND, PEBBLES, OR PIPE SEALANT. TURN THE WATER OFF, UN-SCREW THE HANDLE, REMOVE THE SET SCREW LOCATED INSIDE THE HANDLE BODY, PULL THE HANDLE BODY UP, LOOSEN THE NUT, REMOVE THE SEATS AND STEM AND UN-CLOG THEM.

bad faucet...get new at lowes or home depot

If your water heater is old or has been recently replaced, it will slough off debris that will get caught in the hot water supply side of the faucet. You have to disassimble the faucet and use a dental pic to remove the debris from it. This is a real common occurance. You can also try to flush out that side by removing the parts and then slowly turning on the water without the parts inside. Be careful not to flood your bathroom when you do this. But usually you have to dig it out. I have spent as high as 3 hours digging the liner from the dip tube of a water heater out of a faucet.

Patty,
The price for this item is based on the supplier you purchase them from as Fix Ya.com does is not a plumbing supplier. It is doubtful that you will get much of a discount on the items due to the low volume however some suppliers in the states may offer such discounts You would have to work with them directly to ascertain that and shipping to your location. If you need the name of a supplier that handles that item let me know. Thanks for using Fix Ya.