COMMUNITY FORUM

dtbaker

07:36AM | 09/27/04
Member Since: 09/26/04
5 lifetime posts
Bvplumbing
I just installed a takagi tk-jr tankless water heater. It serves the master bedroom and kitchen, so the size is just about perfect.

I have had some problems with it "cutting-out" after about 10 seconds.

At first I suspected a problem with gas volume as I had left in the terminating section of 1/2" gas pipe and shutoff.... So I replaced with 3/4" per specs.

now.... with the cover off the unit, it runs fine. as soon as I put the cover on, the problem returns! My only suspect now is that the restricted airflow (of the limited intake size on the cover) reduces the o2 just enough to cause the system to error out. possible?

In case you dont know... the tk-jr has a fan-driven intake, and the front cover has a relatively small intake vent area. I have a 7" round vent to the outside... and it behaves the same with the closet door open, so the air available is not the problem.

I live at 7000' elevation. The manual says it should be adjusted above 4500', but the takagi techs told me it is pre-adjusted good up to 10000'.

what do YOU think?

d

LonnythePlumber

08:24AM | 09/27/04
You're beyond my experience. I am certified on some brands but I am not familiar with yours. We usually have to enlarge the gas line from the meter in. Your comment on 1/2" & 3/4" makes me concerned that you may not be sized right. It's not just the last end of the piping, it's the total volume available at the distance from the meter.

The tankless heaters and the new flammable vapor ignition resistant water heaters all have special problem solving and parts differences between the manufacturers. We're going to their sites.

dtbaker

08:41AM | 09/27/04
Member Since: 09/26/04
5 lifetime posts
the gas line from meter to house is 1", then there is a run of about 12' to the heater, most of it was 3/4", and the last bit sticking out the wall had a reducer elbow to 1/2 and a stopcock.

I replaced the 1/2 section with 3/4, and used a full-flow ball valve, so gas *should* be fine. I also tested by turning on all other gas appliances in the line when the unit was running, and it was fine UNTIL I repeated my test with the cover on?!

I think I have a 15psi pressure gauge I could tee into the line to see what it is during operation, but I am highly suspect of the air o2 content at my 7000' elevation.

There are two little adjustment screws on the manifold, but I hesitate to mess with them without knowing what to look for or tell how to get it "right". I am very tempted just to drill some more holes in the cover to provide a little more flow, but I'd prefer to get a better answer. ;)

LonnythePlumber

08:50AM | 09/27/04
I believe it is primarily an air adjustment or something to do with elevation. I would read your owners manual or go to their site.

Secondly I am commenting that I don't think your gas line is big enough unless you have a small unit. You take the lenth of the line from meter to the heater. How many BTU's total is taken from that line and you get the size of pipe needed from the sizing charts.

dtbaker

09:01AM | 09/27/04
Member Since: 09/26/04
5 lifetime posts
the tk-jr is the smallest takagi unit (140000btu max), and the specs are for 3/4", so I think I'm fine with the gas with the runs I have according to the charts.

their manual talks about adjustments over 4500' elevation, but gives no details what it is supposed to be.

I've been poking around on the web, and found a boch installation manual online that specifically states the ****** pressures, and that the inlet should be adjusted down 4% per 1000' elevation. but MY manual doesnt give any details. The takagi tech support has not given any details either.

I would LIKE to check/adjust it myself, but want to get confirmation that its "ok" to do it, and also find out what kind of little gauge I need to go out and get to do it properly.

LonnythePlumber

09:32AM | 09/27/04
You are probably right about your gas. If you have a run of 50 feet from meter to heater then you can have 152,000 BTU's. So if you have no other gas outlets in the structure you should be okay.

I cannot help on the elevation adjustments. Perhaps another poster has experience.

dtbaker

09:41AM | 09/27/04
Member Since: 09/26/04
5 lifetime posts
I found a Boech installation manual which states that manifold pressure should be reduced by 4% per 1000' of elevation, which means that I *should*? reduce mine from the default 2.8"WC (sea-level natural gas setting) to 2.0"WC by my calculations.

problem is, I don't know what kind of gauge I need, or any other tips I might need to do this safely and effectively.

anyone....?

d

kbybee

08:58PM | 07/27/06
Member Since: 07/27/06
1 lifetime posts
I also have the Jr. Propane model. I am at 1600 feet above sea level and I have had the same issue. I called the support line and they told me it was censor that regulates the on and off of the flame. They told me that we have to sand off that censor. That worked but we have to sand it off every couple months. We are not happy with having to do this so often. It makes plenty of hot water when it works. I have searched the web trying to find a better replacement with no luck. The support guys are asian and very hard to understand. If anyone has an idea on how prevent this problem let me know. when you pull off the cover you can see a small metal plate with a eye glass where you can see the flame the censors are passing thru that plate. The censor on the left is the one giving the trouble, however I always sand them both. Oh! Be careful wne you pull off the plate the eye glass falls off when you remove the plate so be careful . Also the gasket around the plate tears easily. Be sure to unplugg the unit and turn off the gas or trip the breaker before servicing.

thanks,

Kelly Bybee

dtbaker

05:53AM | 07/28/06
Member Since: 09/26/04
5 lifetime posts
...been a while on this issue, but the resolution was to flip a 'dip switch' that disables the back-pressure sensing. The gas supply was not a problem at all, but for some reason the system detected restriction in the exhaust line.

while disabling the sensor is maybe not the safest thing to do, the unit has run without a hitch ever since.
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