Takagi TK2 vibration/unstable flame

Users who are viewing this thread

single_digit

New Member
Messages
29
Reaction score
0
Points
1
Location
Louisville, KY
I have a TK2 that is approximately 9 years old. It has two quirks that started a while back and that I would really like to resolve. Maybe they are related, maybe not.

The most important problem is that when the unit is first fired up (my wife takes HOT showers in the morning), if the water is turned on more than a small amount the TK will start to rumble and vibrate horribly (it sounds almost like a special effect out of a movie). If allowed to proceed it sounds like it would rip the plumbing system apart. If the water is allowed to warm up before running wide open, there is usually no problem. When the flame window is viewed the flame goes completely chaotic inside. I called Takagi and they said it was most likely because my intake pipe was too close to the exhaust, so I rerouted my intake (3" PVC) to turn downward and it is now several feet (~4') from the exhaust vent. This did not solve the problem. Another suspicion was the gas flow was insufficient. I have 3/4" gas line all the way to the heater and this happens when no other appliance is using gas. The problem did not occur when first installed so I don't believe it to be a problem of the line delivering too little gas. I don't have a remote so I can't pull a code (unfortunately I don't recall if the LEDs changed or not during the vibration). My suspicion (and Takagi tech suspected as well) is that this is somehow an issue only when running full combustion (wide open). Though it doesn't strictly seem to happen that way (it has occasionally acted up mid-shower without changing settings, but this is rare). I have recently done a vinegar flush and saw very little difference (very little buildup despite not having flushed it in a long time).

Second problem is that occasionally mid shower the heat will drop out for a few seconds and then come back.
You can feel the water in the shower getting colder for ~10 seconds before it goes completely cold then comes back. saw this discussion, but I have no idea how to clean the flow sensor. Link to instructions would be great.
Any help would be greatly appreciated. FYI this water heater only services a single bathroom. But the problem has manifested both in the shower and on our jacuzzi tub (ie not the mixing valve in the shower) for the intermittent hot water loss).
 

Dana

In the trades
Messages
7,889
Reaction score
509
Points
113
Location
01609
Unless the TK2 is effectively mounted right AT the gas meter, 3/4" gas line is insufficient to support the 185,000 BTU/hr full-firing rate of the unit without the gas pressure dropping or fluctuating, whether other appliances are using gas or not:

natural%20gas%20pipe%20chart.jpg

Those lengths also include all "equivalent length" per Table A2.2 for every ell & tee between the TK2 and the gas regulator (typically at or near the meter.) The numbers in the matrix are in burner size (x 1000BTU/hr.) For the 3/4" line to be kosher there has to be less than 10 equivalent feet between the pressure regulator & TK2.

Any tees branching off the run to the TK2 can also introduce oddities, since they are effectively resonators that can be excited into a sinusoidal pressure fluctuations, a phenomenon that will vary in likelihood of getting started at different gas flow rates.

Both the gas regulator an the TK2's gas controls will drift a bit in characteristics as they age, and may still be within spec, so just because the problem wasn't happening often early in it's life doesn't mean that the gas supply isn't the problem. If you correct the gas plumbing with a home-run (no branches to other appliances) for the TK2 teeing in as close as you can possibly get to the regulator/meter, with the requisite BTU capacity (with some margin- don't cut it too close), that alone may correct the problem. In most houses that means 1-1/4" gas plumbing straight to the tankless. A 3/4" line would appropriate in fewer than 1% of tankless installations.
 

single_digit

New Member
Messages
29
Reaction score
0
Points
1
Location
Louisville, KY
Unless the TK2 is effectively mounted right AT the gas meter, 3/4" gas line is insufficient to support the 185,000 BTU/hr full-firing rate of the unit without the gas pressure dropping or fluctuating, whether other appliances are using gas or not.
Both the gas regulator an the TK2's gas controls will drift a bit in characteristics as they age, and may still be within spec, so just because the problem wasn't happening often early in it's life doesn't mean that the gas supply isn't the problem. If you correct the gas plumbing with a home-run (no branches to other appliances) for the TK2 teeing in as close as you can possibly get to the regulator/meter, with the requisite BTU capacity (with some margin- don't cut it too close), that alone may correct the problem. In most houses that means 1-1/4" gas plumbing straight to the tankless. A 3/4" line would appropriate in fewer than 1% of tankless installations.

Thanks for the detailed reply. Sounds like the likely culprit. The TK2 is not close to the meter at all. There is 1" line about 10-15' in to the house, but there is at least another 20' of 3/4" pipe with several turns. This is in the closet of our second floor. I would imagine it will be nearly impossible to get sufficient flow from my current line based on that table. Running a new dedicated line would be difficult to say the least.
So it seems like insufficient flow, but it really only seems to materialize when the unit is initially fired up under high demand. Is there a way to set it so that it can't fire enough burners to send it in to the "choke of death"? After a minute or two it seems to work fine regardless of how hot we turn up the water so I figure if I can simply keep it from demanding too much at the beginning, we should be okay. My fallback solution is to run water from our downstairs HW heater (in the basement), but this means the water will likely take over two minutes to get warm. I'd rather avoid this if possible...
Oddly the basement unit is another tankless (Rheem RTG-95DVLN) that pulls more BTU and hasn't had trouble (admittedly with fewer turns and slightly shorter length).
I do not have the control panel, but I know the jumpers can be changed to alter the settings. With or without that panel is it possible to pull back the initial demand for fuel? I suppose another option is to sell of this unit and invest in a smaller unit that pulls fewer BTU. Again, not ideal...
 

Dana

In the trades
Messages
7,889
Reaction score
509
Points
113
Location
01609
The constricting gas lines have both a flow problem (pressure drop) but also a fluctuating pressure component that causes a rapid feedback problem as the tankless modulates trying to compensate, but at a different slew rate than the pressure fluctuations.

With a 185K burner on one tankless and a 199K burner on another you're probably at or over the capacity of the meter. Check that out too.

With the 185K burner in a closet it's very unlikely that it has sufficient make-up air. The minimum cross section make-up air into the closet for a burner that size is 185 square inches, which is an unobstructed 13.6" x 13.6" hole and no grille- it needs to be bigger if there is a grille to account for the reduced free area. To achieve that with a door cut on a 30-32" wide closet door it would take a bottom door-cut 6-6.25" deep (the cats could squeeze in/& out of there with ease).

Take the hint on the front cover of the manual:

"...if the information in this manual is not
followed exactly, a fire or explosion may
result causing property damage, personal
injury or death."

Do your best to come as close as possible to the installation specifications- this isn't stuff to screw around with. If it burns your house down or kills your kid with carbon monoxide poisoning Takagi isn't liable- the installer is.

You can monkey with the DIP switches all you like (but don't do it blindly or you could create a serious hazard). There's almost nothing right about this installation.

Verify that the DIP switch is selected for INDOOR operation, as indicated on p.7.

Do NOT change the switch setting from NG to LP, even as an experiment.

You can change the temperature setting from the factory default 122F down to 113F or 104F, (see p14) without increased hazard, which may or may not affect your start up issues. Lowering the temperature changes the ratio of hot/cold at the shower mixer, which may improve or hurt any modulation issues related to pressure feedback from the shower mixer's anti-scald valve, which may be another contributing vibrational component to the growl.
 

single_digit

New Member
Messages
29
Reaction score
0
Points
1
Location
Louisville, KY
The constricting gas lines have both a flow problem (pressure drop) but also a fluctuating pressure component that causes a rapid feedback problem as the tankless modulates trying to compensate, but at a different slew rate than the pressure fluctuations.

With a 185K burner on one tankless and a 199K burner on another you're probably at or over the capacity of the meter. Check that out too.

With the 185K burner in a closet it's very unlikely that it has sufficient make-up air. The minimum cross section make-up air into the closet for a burner that size is 185 square inches, which is an unobstructed 13.6" x 13.6" hole and no grille- it needs to be bigger if there is a grille to account for the reduced free area. To achieve that with a door cut on a 30-32" wide closet door it would take a bottom door-cut 6-6.25" deep (the cats could squeeze in/& out of there with ease).

The air intake is external to the house (that was what I was talking about with the 3" PVC). Both pipes run straight up through the roof with the intake turning downward to put distance from the exhaust vent. So I don't think the air intake is a concern. The Rheem unit isn't running when we have had issues and certainly it is something we have been mindful of.


You can monkey with the DIP switches all you like (but don't do it blindly or you could create a serious hazard). There's almost nothing right about this installation.

Verify that the DIP switch is selected for INDOOR operation, as indicated on p.7.

Do NOT change the switch setting from NG to LP, even as an experiment.


You can change the temperature setting from the factory default 122F down to 113F or 104F, (see p14) without increased hazard, which may or may not affect your start up issues. Lowering the temperature changes the ratio of hot/cold at the shower mixer, which may improve or hurt any modulation issues related to pressure feedback from the shower mixer's anti-scald valve, which may be another contributing vibrational component to the growl.

I can look into having the gas company place a larger meter, but I think the constrictions inside the house will still pose the bigger problem. I'll look in to the DIP switch settings for temp. Would the remote control panel give me any other control options that the DIP switches don't that could be applicable here?
 

Dana

In the trades
Messages
7,889
Reaction score
509
Points
113
Location
01609
The TK-RE02 displays the numerical error codes listed on p.16 of the manual, which makes debugging a hard-fault condition a lot easier than counting the blinks of the LED. It can also display the sensed flow rate (with fairly coarse granularity), the incoming water temp, and the outgoing water temp. It may have one or two additional output temp settings than you can get out of the DIP switches, still in fairly coarse steps, but that's about it. It's a nice to have (I have one on the KD-20 I'm using as a combi-boiler), but if the thing isn't already shutting itself down and blinking at you, it isn't going to help point to the problem you're experiencing.

A larger meter isn't going to fix anything if you're not running multiple large burners at the same time, but it's code to have a meter capacity that can handle it all being on at the same time. The capacity is indicated on the meter somewhere, as is the input BTUs of the various gas burners in the house. Go around and add them all up, then compare the total to what it says on the meter.

But with the current sub-code gas plumbing you're guaranteed to not have all burners running full out at the same time, which is just as bad (or worse) from an equipment safety point of view as being limited by meter capacity. When the pressure drops low enough the smarts on the tankless controls SHOULD turn it off and spit an error code, but SFAIK there is no guaranteed response time for that. Since it happens even when other burners aren't running, a meter-swap isn't going to fix the symptom, even if it's still a necessary thing to do for other reasons.
 

single_digit

New Member
Messages
29
Reaction score
0
Points
1
Location
Louisville, KY
Eesh. Well I'm definitely going to have some plumbing in my near future. Unfortunately some of it is quite inaccessible.
 
Top
Hey, wait a minute.

This is awkward, but...

It looks like you're using an ad blocker. We get it, but (1) terrylove.com can't live without ads, and (2) ad blockers can cause issues with videos and comments. If you'd like to support the site, please allow ads.

If any particular ad is your REASON for blocking ads, please let us know. We might be able to do something about it. Thanks.
I've Disabled AdBlock    No Thanks