20 Most Recent RTO Takagi Jr. TK-JR-N Tankless Water Heater - Natural Gas Questions & Answers

In my case, the error code 21 was caused by the failure of the vent fan to run-on after shut off (easily verified by listening to the unit). The problem was not resolved by swapping either the fan or the control unit with another heater. I talked to a local service tech who had a couple of suggestions. One was to move DIP switch #6 to the upper position. After doing thisit will be necessary to re-initialize the controll by cycling power off and on. This fixed the problem. I emailed Takagi tech support to ask if I should consider this as permanent fix, or if there was something else I should do. Since I got no reply, I'll pass on the tech's other suggestion: buy a Rinnai.

Flowmeter.....Gas Pressure.....Ignition? I'm not psychic. Tk-Jr is a dependable 140-145,000 BTU 2nd Gen Unit SS Vent , <.82 EF. Failure is a Tech Service issue and the Tech may need Factory Support from California. This is probably a pre-A.O. Smith/Takagi unit Does the igniter spark 3 times than shut down and fan purge HE? Can you smell gas tracer (remember NG/LP is odorless w/o mercapthan in it)? Tech will need a digital Manometer for Line and Manifold Pressure Test. And a Multi-Meter Toll Free # on Unit or in Manual

Yes the faucet could be a problem. Try changing for one which you know is ok.
The long run of pipework - each bend, elbow or joint all have a reducing effect on the flow, maybe enough to matter with a restricted outlet. none of this can be altered except by renewing with larger bore pipe - expensive!
Also there should be a dirt filter in the mains water input line/pipe. Try removing & cleaning. Try also removing , reconnecting and then the hot tap [faucet]

The boiler will have an actuator valve which fires it up when a certain flow of water is reached. If the flow is reduced AND the valve is worn, maybe a replacement. Not sure about it's USA construction but in the UK [it's called a diverter valve] many have a rubber diaphragm which is cheap to replace
Check also if it uses a flow sensor switch
Had a look at the Takagi web site and there are pdf's of manuals
takagi.com
Overall I am still thinking that the main prob is in the flow.
Hope I've helped - come back anytime
Rod.Davies

cold supply may be reduced as long as you give the heater enough flow to work best of luck

Tankless water heaters normally take a little longer than a regular heater to provide hot water because they have to start and get warmed up. I'm guessing the heater uses a pilot light and that the short amount of hot water when you turn on the tap is hot because when the water is sitting still in the heater the heat from the pilot light is enough to get it hot. The tub faucet will get hot a lot faster than the shower because it lets a lot more water through and empties out the pipes faster than the shower. You could probably speed things up by letting the tub faucet run on completely hot for like 10-15 seconds and then turning on the shower.

Remove your hydronic pump and replace the flexible impeller coupling that couples the impeller blades to the pump motor. make sure you don't do this on a sat or, sunday (i hate house calls then) and, be sure you have a new pump housing gasket before you start the job. Also check the unit for loose pipe brackets

Owner Manuals

Bad faucet cartridge: walk-thru on following link http://waterheatertimer.org/Crossover.html If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

What water pressure reading do you have? IS there a mixer in the system? What is the exact model number?