Will a recirculating pump work with a tankless hot water system? I have a tankless hot water heater and don't like the delay in getting hot water. I am considering installing Undersink Hot Water Circulating System. Will the pressure drop from that system pumping be enough to turn on the heater on the tankless system?

Depends how far away the tankless is located.
Tankless are not instant hot water heaters
Also check for cross connection
http://waterheatertimer.org/Crossover.html
http://waterheatertimer.org/Water-heater-recirculation-system.html
http://waterheatertimer.org/How-to-install-under-counter-water-heater.html

Gene

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

Maybe I am not understanding your problem exactly, but if you have the instant hotwater system installed it should be measuring the temperature of the water in the hot water line and if it drops below the set level it should open the hot water side until the temperature is reached. If it was installed correctly it puts the hot water back into the cold water line so it isn't wasted.

Question not 100% clear.

1) The pump is not working? Does the pump make a noise? if pump is not working full-time, it can cause delay in arrival.
If pump motor is suspect, and outlet has power, then check override switch located on timer. Set override to Timer, move some of the trippers outward, then manually rotate timer dial until pump turns ON.
http://waterheatertimer.org/images/IMG_9325-grundfos-timer-800.jpg
If no noise is detected, or noise stops and starts, or seems strained, or if pump is hot, then pump motor may have burned out.

2) If pump is working, and makes noise like a humming sound, and pump motor is not hot, but hot water is not circulating, then unplug pump so it will not overheat and burn up.
Disassemble the pump and cross-over piece. Clean piping with white vinegar or CLR. Do not soak in CLR or it will damage seals. Rinse parts thoroughly. Reassemble and see if problem is resolved.
If pump is vibrating, then suspects include sediment and/or air inside line, and this can be resolved by cleaning as described. Also install air vent to increase life of pump.

3) Other causes for hot water delay at faucet are crossover.
Crossover can be caused by bad single-handled faucet cartridge, and/or by clogged-or-failed check valve on cross-over piece on grundfos.
This type of problem lets cold water enter hot line, and causes delay in arrival of hot water. Clean-or-replace the grundfos cross-over piece, and replace bad faucet cartridge.
Open following link for testing instructions:
http://waterheatertimer.org/Crossover.html

Resources:
http://waterheatertimer.org/Water-heater-recirculation-system.html
http://waterheatertimer.org/pdf/Troubleshoot-recirculation.pdf

Add a comment for more help.

Take a moment and rate answer for accuracy:
And take advantage of fixya expert assistance live.
For a price, expert works with you while you work on water heater or any do-it-yourself project.
Fixya is always less expensive than a service call.

Question not 100% clear.

1) The pump is not working? Does the pump make a noise? if pump is not working full-time, it can cause delay in arrival.
If pump motor is suspect, and outlet has power, then check override switch located on timer. Set override to Timer, move some of the trippers outward, then manually rotate timer dial until pump turns ON.
http://waterheatertimer.org/images/IMG_9325-grundfos-timer-800.jpg
If no noise is detected, or noise stops and starts, or seems strained, or if pump is hot, then pump motor may have burned out.

2) If pump is working, and makes noise like a humming sound, and pump motor is not hot, but hot water is not circulating, then unplug pump so it will not overheat and burn up.
Disassemble the pump and cross-over piece. Clean piping with white vinegar or CLR. Do not soak in CLR or it will damage seals. Rinse parts thoroughly. Reassemble and see if problem is resolved.
If pump is vibrating, then suspects include sediment and/or air inside line, and this can be resolved by cleaning as described. Also install air vent to increase life of pump.

3) Other causes for hot water delay at faucet are crossover.
Crossover can be caused by bad single-handled faucet cartridge, and/or by clogged-or-failed check valve on cross-over piece on grundfos.
This type of problem lets cold water enter hot line, and causes delay in arrival of hot water. Clean-or-replace the grundfos cross-over piece, and replace bad faucet cartridge.
Open following link for testing instructions:
http://waterheatertimer.org/Crossover.html

Resources:
http://waterheatertimer.org/Water-heater-recirculation-system.html
http://waterheatertimer.org/pdf/Troubleshoot-recirculation.pdf

Add a comment for more help.

Take a moment and rate answer for accuracy:
And take advantage of fixya expert assistance live.
For a price, expert works with you while you work on water heater or any do-it-yourself project.
Fixya is always less expensive than a service call.

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

Add a comment for more help.

Take a moment and rate answer for accuracy:
And take advantage of fixya expert assistance live.
For a price, expert works with you while you work on water heater or any do-it-yourself project.
Fixya is always less expensive than a service call.

Open following link for Re-circulation information and resources:
http://waterheatertimer.org/Water-heater-recirculation-system.html

If the unit is getting hot, it may have already slowed and is now spiraling to it end.
Try bleeding air out of water lines, and clean autocirc with CLR calcium lime and rust remover.
Recirculation systems have a built in check valve so cold water side of faucet will work correctly. If this check valve is stuck open or closed, it can affect a lot of things in the plumbing system.
For example, stuck check valve can cause tankless water heater not to operate. It can also cause autocirc pump to overheat.
Lines, or elbows clogged with sediment can also cause same problems with recirculation system. If your system has direct return line to water heater that connects into the water heater drain port, then clog in line can cause overheated pump. Check water flow, check water lines, and clean out autocirc.

Upvote the help.
And take advantage of fixya expert assistance live.
For a price, expert works with you while you work on autocirc or any do-it-yourself project.
Fixya is always less expensive than a service call.

Laing UCT-909-TANKLESS UltraCirc Tankless Water Recirculating Pump

This is designed to maintain the proper flow to fire the heater. Please be sure the pressure in the house is at least 5 psi over the minimum required for your unit.

they have it installed wrong it is pulling from the wrong side, it is supposed to pull ot water up to the fixture but then if it stays hot on the cold side they are backwards

What is your reason to have a recirc line on your water heater does the heater sit to far away from a certain fixture? If you put a pump on your tankless waterheater then your heater will continually fire till the call for hot water is stopped. Yes you normally do need a seperate line installed for a recirc line usually from the water heater to the farthest fixture away. If your problem is taking to long to get hot water then I suggest installing a second heater closer to problem area.

I called Noritz error code 16 is a overheat problem. Noritz say's to flush your coil with vinegar or CLR.
Use a small pump to recirculate the CLR or vinegar through the system for 45 minutes and flush with fresh water. This worked for me.