NEED DIAGRAM ON INSTALLING UNDER SINK INSTANT HOT WATER CIRCULATING SYSTEM?

Yes... it works with dual handle or single handle
The built-in crossover valve on autocirc accomodates the flow differential between hot and cold water draw.

http://waterheatertimer.org/Water-heater-recirculation-system.html
http://waterheatertimer.org/9-ways-to-save-with-water-heater.html

Gene

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

http://waterheatertimer.org/Water-heater-recirculation-system.html#laing

Gene

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

Crossover valve went bad
There is no replacement part
http://waterheatertimer.org/Water-heater-recirculation-system.html

Gene

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

http://waterheatertimer.org/Water-heater-recirculation-system.html
http://waterheatertimer.org/Crossover.html

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

Must replace tank.
Insinkerator stainless steel tank does not have anode rod to protect against depleted tank wall.
Copy following link for tips installing under counter heater, and manuals for several different brands
http://waterheatertimer.org/How-to-install-under-counter-water-heater.html
Add comment as needed and fixya will not send me email to reply with more detail

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

Question posted under autocirc recirculating system.
Unknown if system has been taken apart and cleaned with white vinegar, or if faucets are single-handled.
Open following links to help isolate possible problems.
http://waterheatertimer.org/Water-heater-recirculation-system.html
http://waterheatertimer.org/Crossover.html

If you have the same Autocirc product I have, then it cannot be taken apart. The timer seems to be connected and sealed together with the pump. If yours is different, answer back with the wires that you can see and we'll see if the timer can be by-passed.
http://waterheatertimer.org/Water-heater-recirculation-system.html

With the ordinary Grunfos-type pump that is not on a timer, you can add a switch and have the pump work on demand as you describe.

And they make a product that does the specific job you describe. It's called a Demand Pump. Link above shows two different types at page bottom.

I have not tested either Demand Pump shown. They operate on-demand ... when you activate the pump, the pump quickly brings water over from the hot water heater.

So the Demand Pump has a higher volume pump than the Autocirc or Grunfos.

I question a two things about the Demand Pump. 1) How will the increased pump pressure affect local pipes, especially supply tubes under a sink. 2) How HOT does the pump get? If pump gets hot, and it is located under bathroom sink next to paper goods, then that is a hazard. Some regional building codes don't allow ceiling light bulbs in closets because the bulbs get hot and start fires when people pack their closets full.

if you had a "pop" and lightning from the timer....
the water got into the electronics.
its time to replace.
getting hot.... was the cartridge either spinning dry, or spinning but not able to move water, did you have a valve off somewhere?
you might call laing or one of their distributors and see if its under warrantee.
where are you located, I can probably help you find a distributor.

Isn't the undersink unit hooked to the cold water pipe? If this is the case, the undersink unit is not affected by the tankless unit!

A Metlund or Taco D'mand system will work Be sure to size it for the correct lenght of the run to the farthest fixture .