Heater turning off

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ugean

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Hello,

I saw some other questions for my heater on here and figured I would sign up and ask about my problem. I have a
Takagi T-KJr2-IN-NG Indoor Tankless Water Heater, Natural Gas
system I installed about a week ago. I did the job myself, and please don't say get a professional. I've done plenty of plumbing in the past and will continue to do it myself. I'm a mechanic and own all the tools I need for the most part. I'm not your normal home owner. I do all my own construction too.

The heater was working fine for a week passed all startup tests. It has 3/4" gas line (freshly run I did all my own threading from stock) connected with a flex line; no leaks. 1/2" water as that is what my whole house is plumbed with, its an old house. Ran a new electrical box. Vented with 4" double wall. Immediate 90 then 24" out an old window above the unit. Terminal outside with a blowback valve built in.

Yesterday it started acting up. If i exceed 3.2 GPM the burner shuts down and fails to reignite giving me an error code 12 "loss of flame". So I did some trouble shooting. No other appliances are on all testing is done and the sink 10' away. Below is what I have done:

Cleaned inlet filter (It was clean)
Disconnected gas line and inspected screen it is clean.
Reset unit of course
Inspected vent line no issues blows out just fine.
The book says to test part #'s 412 (flame sensor) but does not give the specs.
Says to check a bunch of the wires everything checked out.
Doesn't look like there is anything wrong with the board.
Flame rod looks good (its brand new).
Flame looks good through the viewing window. Blue maybe occasionally a flicker of orange but doesn't appear to be any lift off.

Settings 122 degrees input temp 68 output temp 118-122

With #6 switch off
1.8-2.9 GMP it works fine
3.2 GMP it will run for anywhere from 1-3 minutes lose flame but reignites and runs fine.
3.4+GPM will run for 30-60 seconds lose flame and fail to reignite.
Max output I have achieved is 4.2 but generally runs at 3.9. Lowering output temp seemed to help but not anything really measurable.

With #6 switch on
1.8-2.9 GMP will run for 30-60 seconds lose flame but reignites and runs fine.
3.2+ GMP will run for 30-60 seconds lose flame and fail to reignite.

I do not have a manometer to measure gas pressure but I live in the city and have never had issues before. The tech support for the heater is closed until Monday. Luckily my shower runs at 2.9 gpm but the faucets full on are 3.2 gpm. Any help is greatly appreciated.
 
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Dana

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OK, to start with you can't reliably run a 140,000 BTU/hr modulating burner like that on the TK-Jr off a 3/4" gas line, unless it's extremely short and straight shot to the meter/regulator, with no tees off to /from other appliances.

The maximum lengths in this chart includes "equivalent feet" for every ell & tee on the system, so for 3/4" iron you're looking at another 4' per ell. The number in the boxes are in thousands of BTU/hr.

gas-natural-piping.jpg


Almost all tankless installations in real houses need a home-run of 1-1/4" gas line to the meter, with nothing else tied into that run. Some can get way with 1", but almost none work reliably on 3/4". The modulating burner are very sensitive to low fuel pressure and to sudden changes in fuel pressure. The fact that it seemed to work fine for a week isn't really an indication that it was working correctly, nor the fact that it's misbehaving even when no other appliances are being used but you probably didn't damage it. When it hits a certain firing rate on a too-small line there can be pressure-resonances in the pipe that leads to fuel pressure oscillation & flame out.

Map the fitting and lengths between the tankless and the meter/regulator and give yourself some margin on that chart. eg: Say you have 63 equivalent feet if it's 1" plumbing that's theoretically good enough, but only barely. You'll be better off if the BTU/hr ratings in the chart for your equivalent length are at least 30% higher than the max BTU/hr of the burner, to KNOW that it'll work. Even as a DIY you don't want to do it more than twice!

Do you have a picture of the installation to share, in case there are any other less-obvious gotchas (or more serious gas-fitting hazards) in the setup?

BTW: I didn't find any functional description associated with switch #6 in the manual, but if you have a better technical manual than the online version, what is switching it on or off SUPPOSED to be doing?
 

ugean

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Thank you for the reply. The manual called for 3/4" line and my whole house in from the meter is only 3/4". I'm not sure how feasible going up is going to be. I appreciate the information and respect what you're saying. But the cost of upgrading the whole gas line far outweighs the value of the unit. If it comes to that I'll have to return the unit.

The line comes in from the meter about 30' T's one way to the Dryer (about another 15' of 1/2") the other goes 4' T's to the furnace (2' of 1/2" down) and about another 20' to the heater (all 3/4"). If I'm following you correctly based on the chart I'm at 82. 82 what? I understand that the unit was supposed to be the first thing off of the line and that if something kicks on while the unit is running I could have problems. But right now nothing else is running. That is something I accepted at installation as tapping in prior to the furnace meant a lot more work and additional expense.

I did call the company yesterday and they said it was a classic sign of not enough pressure. They said I needed 5.5"-10.5" of pressure. I'm borrowing a manometer from a friend today hopefully so I can get the pressure readings. I called my service provider and they said they would come out and adjust up the pressure and sent me the paperwork. The paperwork says the standard is 6" of pressure elevated is 11" but upgrading to the 11" costs $300. There goes any savings this unit was going to provide me. I checked the actual meter and it is rated for 5". So I'm going to at least have them get me up to the standard.

I found online that changing the #6 switch to on is an adjustment for mounting the unit outdoors and changes the way it calculates its airflow. Cooler outdoor air is more dense. I figured since it was an old basement and the temperature had dropped outside that maybe it was effecting it. Just something easy to try.
 

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The manual doesn't specify a 3/4" line, only a 3/4" connection.

At 82 equivalent feet 3/4" line is only good for about 74,000-75,000 BTU/hr draw, and that's with a dumb on/off burner, not a sensitive & reactive modulating burner like a tankless. Even 1" line won't be quite good enough, but it probably won't mis-behave as much, since it's only good for 140,000 BTU/hr @ 80 equivalent-feet. (The equivalent lengths change with pipe size.)

As with most tankless installations, you need to tap in as close to the meter as you can, and run a dedicated 1-1/4" line to the tankless, if that dedicated line will also be 82 equivalent-feet. It's fine if it's tapping in near the meter with very short run of 3/4" and at the tankless end, but the majority run in the middle needs to be an un-interrupted 1-1/4". If it's possible to plumb a dedicated run in 1" that comes in under 60 equivalent feet you'll probably be fine with 1". You don't have to upgrade the lines to anything else, but you may have to cut into that initial 30' run at the meter end, teeing into your new home-run line dedicated to the Takagi.

What this is NOT is a pressure problem at at the meter. They'll run just fine at slightly low pressure as long as you feed it in an appropriately sized pipe for the BTUs and equivalent length. It's up to you whether the cost of running a dedicated line to the Tagaki, but that's the real solution. There's nothing you can do on the meter end that will make it work correctly over a realistic range of operating conditions.
 

ugean

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Thank you for the information. I got a manometer from a buddy. I figure I should at least do my due diligence and test the pressure it isn't going to cost me anything. Likewise having my meter upgraded to 6" isn't going to hurt me. I would like to put in a gas oven at some point. If that doesn't do anything then I'm going to have to see if I can return the water heater or sell it on ebay. Running a new 1" (or larger) dedicated line is out of the question. The ROI on that pipe and time to install just isn't there. I was questioning if it was there for the recent install.

Also my furnace is just an on/off burner at 75,000 BTU's.
 

Reach4

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I was questioning if it was there for the recent install.
http://www.takagi.com/media/54102/60Z101.pdf
The warranty will not cover​
    • Installation and service must be performed by a qualified installer (for example, a licensed plumber or gas fitter), otherwise the warranty will be void.
    • Introduction of hard water measuring more than 7 grains per gallon (120 ppm) for single family domestic applications
    • Gas: incorrect gas pipe sizing, incorrect gas meter sizing, incorrect gas type, and/or gas pressures that fall outside the product’s specified range
 

Dana

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The manometer is only going to tell you what's already dead-obvious to every fraternity brother: You can't chug a beer in 3 seconds through a straw- you need a appropriately sized pipe.

The pressure drop across the gas line between the meter increases with the firing rate, and you have barely sufficient pipe capacity to support HALF the firing rate of the TK-Jr, let alone the TK-Jr plus any of the other appliances teed off from that line.
 

ugean

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It makes sense I understand. It is just that the ROI is not there on upgrading the piping. I wish I had known that it was going to require that before purchasing. I would not have purchased it.
 

ugean

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Wanted to post a follow up to this with the outcome. Gas provider came out. Pressure at the meter was 5.7. They up'd it to 7 and still had problems. Takagi sent a tech from local plumbing company out. They tested everything with the unit and it all checked out. They then tested the pressure at the unit. It dropped significantly at low burn then out of spec at high burn. Guy was nice and still didn't charge me.

Problem turned out to be a filter in the flex line was restricting the volume. The flex line was rated for 250k btus but it wouldn't supply enough volume for 140k. I replaced the flex line with 3/4 hard line and problem solved. No need to replace all the line with a bigger line. Unit even works fine with the furnace and dryer running and they are before the unit in terms of flow.
 

Reach4

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Problem turned out to be a filter in the flex line was restricting the volume. The flex line was rated for 250k btus but it wouldn't supply enough volume for 140k. I replaced the flex line with 3/4 hard line and problem solved.
Wild. Do you have information, such as brand and model, for that flex line with a built-in filter?
 
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