need help with poor burning Takagi tankles

[passinthru]

OK,
I just installed this last fall for my in floor heat system, and it has
not run properly since. Model T-K4-IN and hooked up useing there
direct-vent concentric termination system,which I think might be the
problem.

When I first fired it up with the cover off it ran fine till I put the
cover on, then it thru a 99 code and shut down. 99 is imperfect
combustion. A few more attempts with the same results so I left the
cover off.A call to there cust.serv. the next day was a waste of time,
so I just run it with the cover off.

I run it this way most of last winter, but it would still shut down
occasionlly with the 99 code.It finally shut down this spring &
would not start, I looked in to the burner and it look's like its full
of charcoal. I procrastinated till now, and its getting cold again, so I
need to get this working. Can I **** this filth out of the burner or do
I need to pull the burner out some how?

There is no blockage in the intake pipes, and gas pressure checked
good. Any help would be appreciated

 

[usa#1]

I would call the manufacturer and ask for tech support.

 

[passinthru]

Ya, maybe I should give that a try again.
Last year the guy I got didn't know nothing about there direct-vent concentric system.

 

[passinthru]

OK.
I got the burner out and cleaned but the heat exchanger looks nasty.

Can anyone tell me does it look like this from bad burning,or does it look like it was leaking?

Thank's

 

[anthony666]

you're pulling exhaust back into the burner and its carboning up .. check out where the venting terminates .. it needs to end somewhere its free to escape, and conversely also somewhere the prevailing wind isn't blowing it back down the intake

 

[passinthru]

Thanks anthony666
My first picture shows the termination, its on the east side off the garage and 200' from the nearest house.
It is however only 12" above the ground where it comes out,but the ground drops down and away quickley. 12" was the min allowed in manuel.

You dont think it could be leaking from inside the concentric do you?

Thanks for the help.
Tim

 

[usa#1]

If the combustion air source is the flex hose, could you not remove it and just pull the combustion air from the interior space where the unit is mounted. That would eliminate the potential of getting exhaust gas pulled in for the combustion air. I have used the same model as you have but I pulled the combustion from the interior space.

 

[Jackfre]

I doubt even with a thorough cleaning that you will save that HX long term. It shows as carbon build up but also looks like moisture has built up and been evap'd off. Does your vent grade to the outside? It should. That prevents any condensation at the termination from draining back into your HX.

The 12" clearance from the ground is a minimum and is only a portion of the code and installation instructions. It is 12"...or above snow load level. Get the snow up around it and it will pull moisture in.

To clean those burners I would suggest that you remove the strap that holds all of the individual burners together. Note where the flame Rod and sparker are and which burners service that area. When you have cleaned all of the individual burners move those low fire burners off to the side of the tray on re-assembly. The way I clean that type burner is with compressed air, a stiff brush and I will gently tap each individual burner on its face to get any precipitant out. It will come out like a white powder or chunks of it.

I would check the gas pressure on this unit. You absolutely do have a combustion problem. Was that unit converted? Was it properly done?

 

[passinthru]

I doubt even with a thorough cleaning that you will save that HX long term. It shows as carbon build up but also looks like moisture has built up and been evap'd off. Does your vent grade to the outside? It should. That prevents any condensation at the termination from draining back into your HX.

The 12" clearance from the ground is a minimum and is only a portion of the code and installation instructions. It is 12"...or above snow load level. Get the snow up around it and it will pull moisture in.

To clean those burners I would suggest that you remove the strap that holds all of the individual burners together. Note where the flame Rod and sparker are and which burners service that area. When you have cleaned all of the individual burners move those low fire burners off to the side of the tray on re-assembly. The way I clean that type burner is with compressed air, a stiff brush and I will gently tap each individual burner on its face to get any precipitant out. It will come out like a white powder or chunks of it.

I would check the gas pressure on this unit. You absolutely do have a combustion problem. Was that unit converted? Was it properly done?

Thanks for the help.
It deffinetley had moisture in it. I took the whole thing apart,and the exhust cap above the HX had rust underneith, with 3 pin holes in it already

The exhust does vent to grade outside.

I did check the gas pressure when it was running and it checked good.

It was bought new as a NG unit.

The HX was really clogged up with that green ****. I used CLR and simple green with brushes,picks,and air but still cant get it clean.
Are you saying that because off the green **** that the HX will probably rot out in short order?
I cant believe this thing didnt even run 6 months.

Should I look into replacing the HX?
Thanks

 

[Jackfre]

Well, the vent is shot. It will only recirc flue gases more than all ready doing so. That vent must grade to the outside from the 90 at the top. As to the HX, you will not get much out of it. Yes, there will be hot spots and they will lead to a leak. As well in your efforts to clean it you bend fins and that too contributes to hot spots. I am not sure on the Takagi, as I've never had one apart, but look below the burner area to see if moisture migrated to the lower section too. Clean your inducer fan and make sure there is no debris or deposits below the burner. Make absolutely sure you have two things on this unit. Number one, a complete gasket kit. Most of them are one shot. As well, get a good CO detector in the area. That should be step one. The CO levels that thing has been running at will blow your mind.

I know that a lot of guys have run these tankless units as boilers. Some work! My experience with them (+100,000) in my old territory is that they are problematic at best. The likely cause of your condensation is continuous firing on low fire compounded by short cycling. Tankless water heaters have a min flow and a min firing rate to initiate operation. Check your units specs. It is probably in the neighborhood of 15kbtu and .6 gpm. If you look at the GPMXDeltaTX500=BTU and push the numbers around a bit you will get an idea what is going on with the system. You should be able to read the flow to a tenth of a gal off the controller. We then have to look at pump sizing. What is your delta T across your loops. Check this not only on a cold slab start, but as the system comes up to temp. If you are over pumping you aren't getting the temp drop across the unit and that to drives the Takagi crazy.

What can you do system wise? You might try a buffer tank of 10gal or so and put a pretty hi make/break aqua stat on that pump ( between the tank and Takagi). This effectively gives you a primary secondary piping set up, which should relieve some of the stress on the tankless water heater. Net/net it is a water heater. It is not a boiler.

You are going to need gaskets anyway. I'd call and raise some hell, nicely at first and see if you can get the parts for free. I will say that there is no way that vent should have deteriorated in that fashion and at relative light speed.

We have a few guys here who will likely make some additional or better system recommendations. Good Luck!

 

[big.jim]

you say it was bought new as a NG unit , are you running it on NG or propane and if propane has it been converted to run propane, what has happened to your warranty ,will the manufacturer not honour it because not installed by a registered engineer?

 

[passinthru]

you say it was bought new as a NG unit , are you running it on NG or propane and if propane has it been converted to run propane, what has happened to your warranty ,will the manufacturer not honour it because not installed by a registered engineer?

I am runing on NG.
I did call them back and they are more helpful than last year . But they want me to clean it and get it running so they can see what its doing.
Thank Tim

 

[Jackfre]

I am assuming that they issue service case numbers. At this point, document, document, document. At least you want a new horiz termination on that thing.

 

[passinthru]

I am assuming that they issue service case numbers. At this point, document, document, document. At least you want a new horiz termination on that thing.

I dont think they gave me a case # but they sent me an email on how to get the burner out.
The problem is I bought it a little over a year ago. I never dreamed it would have been in this bad of shape,or I would have checked it out this spring when it quit running.
I have to wait till tomorrow to call them back.

IIRC when it was running last winter, I had stat. at 65*-output temp set at 111* input was about 77*..Pump was at 2.6 GPM. I dont think it did any short cycling, it seemed like when it fired up it would run for a few hours, then it would be off a long time.

 

[brewchief]

How big of space are you heating? What is it's calculated heat load?

I think part of the problem is you have a unit that's way to big so when it's running it's running at it's lowest input, most modulating furnaces/boilers/water heaters will not have that great of combustion at low input levels.

I like Jackfre's suggestion of a buffer tank, that will let it fire at a higher input for a shorter time.

Is there a way on the display to read what rate of fire it's running at when it's running?

 

[passinthru]

How big of space are you heating? What is it's calculated heat load?

I think part of the problem is you have a unit that's way to big so when it's running it's running at it's lowest input, most modulating furnaces/boilers/water heaters will not have that great of combustion at low input levels.

I like Jackfre's suggestion of a buffer tank, that will let it fire at a higher input for a shorter time.

Is there a way on the display to read what rate of fire it's running at when it's running?

1440' is actual floor size. The design co. used 1600 sq. ft. and said 40,000 BTU were req... They recommended this heater. Its a 11,000-199,000 BTU.

You are right though, everytime I look in the burner only about 1/3 of it is burning.I dont know of a way to check that on the display, but I will ask when I call them tomorrow.

Thanks Tim

 

[Jackfre]

Use the formula I gave you. It will tell you at what rate it is firing. The issue with most of these is that with the flow rate and delta T they are hardly ever above low fire.

When you look at tankless water heaters they are designed to have widely variable flow and high delta T. In a closed loop hydronic system you get fixed flow and low delta T. Completely the opposite of its design parameters. At 2.6 gpm and a 20* delta T you are at 26000 but input. As your delta T diminishes the unit has to decrease its firing rate. At 26000 input you are at 13% of the units capacity.

Some folks say they have good luck with tankless in a heating application. I am happy for them, but don't get it.

 

[mygarageone]

Use the formula I gave you. It will tell you at what rate it is firing. The issue with most of these is that with the flow rate and delta T they are hardly ever above low fire.

When you look at tankless water heaters they are designed to have widely variable flow and high delta T. In a closed loop hydronic system you get fixed flow and low delta T. Completely the opposite of its design parameters. At 2.6 gpm and a 20* delta T you are at 26000 but input. As your delta T diminishes the unit has to decrease its firing rate. At 26000 input you are at 13% of the units capacity.

Some folks say they have good luck with tankless in a heating application. I am happy for them, but don't get it.

Why then does the manufactor show this unit being used for radiant floor heat ?
They must know the unti will fail using it for this purpose.?

 

[Jackfre]

Why do they allow it? Well, it may have something to do with sales. I am always surprised to hear it, but there are guys here who say their "tankless as a boiler" works well. You cannot argue with success, but I don't understand it.

 

[mygarageone]

Why do they allow it? Well, it may have something to do with sales. I am always surprised to hear it, but there are guys here who say their "tankless as a boiler" works well. You cannot argue with success, but I don't understand it.

I ask my supplier about this unti being used as a boiler , he said lots of guys are using them with success , but who really knows For sure.?

 

[passinthru]

GOOD NEWS::
There going to send me a new HX. He said he doesn't have a recoard of me calling last year,but it shouldn't have rotted out that fast.
He said the new ones have a damper built in them,so they must of had some kind of problem.

A couple pics of exhust vent.

 

[mlyonsdc]

Can I ask how it is working today? I am looking at options for a 4 zone slab floor in my new garage. We just poured the floor yesterday.
Thanks