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Phil
Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 7910
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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I have a T-K Jr. about 6 years old. It fails to start when

Customer Question

I have a T-K Jr. about 6 years old. It fails to start when drawing water from the longest run. The fan starts, I hear clicking sounds, the fan stops and the led give 3 flash pattern. Sometimes there is a brief odor of gas. I measure the flow at this faucet at over 1 gpm using a container and watch. Closer fixtures don't cause the problem.
Submitted: 1 year ago.
Category: HVAC
Expert:  Phil replied 1 year ago.

Hello, the odds are nearly 100% that the heat exchanger is fouled with hard water scale to the degree that the extra resistance to flow in the longest run is not allowing the flow switch to close and send power to the gas valve.

Tell me if you feel like setting up a acid flush operation and acid flushing it yourself or if you need a list of well rated plumbers in your area.

We can go from there without a time limit.

Customer: replied 1 year ago.
As I mentioned on the inquiry form re what I had tried so far, I removed and inspected both thermistors and found no sign of scale. I am getting over 1 gpm at the far fixture. With a measured lower flow at the near fixture the unit operates properly.
Expert:  Phil replied 1 year ago.

Hello again,

The thermistors are not heated surfaces and do not accumulate hard water scale as fast as the heat exchanger surfaces.

Not much else would cause the problem than a scale restricted heat exchanger...it is a pervasively common problem. The only doubt is raised by your 1 gpm measurement at that hot water tap... in light of all the other taps flowing enough water to close the flow switch, it still looks like the heat exchanger has water scale in it... some scale could be fouling the flow switch slightly as well, exacerbating the problem.

https://www.youtube.com/watch?v=Y7DUH2NIA0c

Let me know if that looks like your unit or not, we can go from there without a time limit.

Customer: replied 1 year ago.
that is the unit, and the name plate gives the model number!
The unit tries to start. The fan comes on, then stops and indicator light emitting diode gives the three flash sign. The manual give 5 possible faults. None of them say anything about flow restriction.
It seems to work fine for a closer faucet set to about half the flow of the far faucet.
Expert:  Phil replied 1 year ago.

The error codes are quite valuable.... about 50% of the time, the rest of the time they are not accurate.. the fact that you only have this problem on the longest run of hot water line only, more or less puts all the nails in the coffin so to speak... it is conclusive to the 99.9% level that there is a restriction either the heat exchanger or the cold water inlet screen, or both.

http://www.takagi.com/media/48366/T-KJr-Manual.pdf

see page 16

Now I could be wrong, but I have been in this business for over 51 years now, and consulted nationally for the last 20 years of that.. and now for the last 5 years have been taking questions on Just Answer here, with a 98.8% positive rating... (6,000 ratings so far)....

given the pervasiveness of heat exchanger fouling and the fact almost nothing else would cause the problems you are having, I am assuming that the error codes, as is very often the case, are not accurate here.... the fuzzy logic chip in their diagnostics software is guessing...

https://www.google.com.gt/?gws_rd=cr,ssl&ei=Q4-nU7v2HZDIsASRvoCwAg#q=fuzzy+logic+error+code+IC+chips

The older your water heater is the more likely it is have water scale fouling, it is also possible that cold water inlet screen needs to be cleaned as well... that will be worth checking first.

http://www.takagi.com/media/48366/T-KJr-Manual.pdf

Customer: replied 1 year ago.
I had already checked the filter and it was clean as new. It started exhibiting the same symptoms on the near faucets intermittently and now constantly. I followed up on the diagnostic light clues. The high limit switch (part 132) tested ok, but the overheat cut-off fuse (part 130) that is wired in series with it tested open. Searching on line I found others with similar symptoms replaced this item to fix the problem. I'm guessing this is the problem and will jumper past it tomorrow to find out.
Expert:  Phil replied 1 year ago.

Hello again, if the high limit switch is starting to wear out, and trips prematurely, then replacing it will solve the problem for a while but it will not solve the cause.... the cause is established conclusively by lower water flow in the long run of tube to the hot tap.

If the over heat fuse blows, it will stay blown, and no allow the heater to resume heating at all until it is replaced...you had reported earlier that the heater would resume heating for a while after it tripped.

It is possible that fuse has since blown, however, if it has nothing would work at all.

Regarding data on the internet, it can be very good and accurate at times, and entirely or partially bogus at other times, or just not fully accurate to your situation as is most likely this time.

very few of those posting on the web are with verified credentials (as with us on Just answer we are all very thoughly vetted, and most of us with 98% or better accuracy scores... my accuracy rate is 98.8)

Thanks for letting me work with you. When we are finished, if my answer has been polite, professional,and thorough, please click one of the ratings . If you still need help let me know!. Expert is not paid for assisting you until you rate answer. Feel free to follow up for30 days at no additional cost.

Customer: replied 1 year ago.
I bypassed (jumper) the overheat fuse, and proved that it was not the problem. The open reading on it proved to be due to the connector channels being too small for the test probes to make good contact. Thinner probes confirmed it was ok.
The high limit switch doesn't trip (pop out) or need to be reset.
Acid flushing the system also did not solve the problem.
Careful flow tests show that it takes over 1 gpm to get it to start. Specifications say it should come on at 0.75 gpm and stay on unless the flow drops below 0.6 gpm. All fixtures are "low flow" except the tub, which doesn't exhibit the problem. I have ordered a new flow sensor to see if that solves the problem.
Expert:  Phil replied 1 year ago.

Thanks for all those tests. The flow sensor could indeed be wearing out or as mentioned earlier by fouled with water scale, it is worth a try, especially since you have certified that it does not close below 1 gpm.

Thanks for letting me work with you. When we are finished, if my answer has been polite, professional,and thorough, please click one of the ratings . If you still need help let me know!. Expert is not paid for assisting you until you rate answer. Feel free to follow up for30 days at no additional cost.