Water Going Cold with Takagi Tankless

[monty]

I have a 5 year old Takagi Tankles (TK1s) that has been operating well for the past years. In the past months we have been having intermittent problems of the water going cold while showering and filling a bath tub in 3 separate locations.

I don't see the problem with a standard hot only faucet on my sinks - just with our mixing valves in our Showers & Tubs. I am wondering if there is a problem with the Takagi now.

I have replaced the thermostatic cartridges in the bathrooms in question and it doesn't seem to be the solution.

So my question is what can I do - I can't always run into the utility room when it suddenly goes cold to see if the Takagi is running, and twisting the temp dial back and forth on my valves will usually cure the problem (minus the cold water sandwich).

My unit has never been serviced beyond cleaning the inlet screen, and flushing it out periodically. I do have hard water - so I would suspect that there is some scale build up, and it has never been de-scaled.

Thanks in advance.
Monty

[Dana]

So, is the Takagi flame turing off when that happens?

If yes, does it fire up instantly when you open a hot-only tap, or is there some time-out period?

Do you have a remote control wired to it?

If yes, is it reporting an error code?

Scale-up isn't a the most likely culprit here, but you should de-scale it anyway. If it's scaling up enough to restrict flow, it could indeed be contributing to the problem. Scale buildup often results in lower heat-transfer efficiency- a more common symptom is the thing fires up, but not enough to provide enough heat at the higher flows even with flame at high. But in warm-water areas this might not be noticable until it's nearly blocked(?).

The TK1 doesn't regulate well at very low flow, and may be turning itself off if the hot-water side flow at the mixing valve is too slow. The fact that monkeying with the valves seems to "cure" the problem makes me believe this is in fact what is happening- when the HW flow gets high enough to re-fire you're back in business until the flow gets low enough that the flow sensor thinks it's stopped, or it can't keep the temp within-bounds at that flow and turns itself off.

The solution may be turn down the temp on the Takagi a notch so that you're running the mixers at the tubs it's a consistently higher hot-side flow. It takes 0.75 gallons per minute to start it up, and needs 0.6gpm to STAY lit. On the TK1 you need the remote to be able to raise or lower the 120F pre-set, but it's worth installing anyway since it can report self-diagnostics. (Search the internet & auction sites for the TK-RE01- it costs less than a single service call.) If you don't already have it, download THE MANUAL.

Yours is old enough to run into flame-detector issues (usually fixed by cleaning with a fine plastic scouring pad- nothing too abrasive) but that's not likely to be the problem here, since IIRC it won't refire without cycling the power to the unit if the controls have that error.

[monty]

Thank you for the quick response:

"So, is the Takagi flame turing off when that happens?

If yes, does it fire up instantly when you open a hot-only tap, or is there some time-out period?"

I will double check (sometimes hard in the shower when it goes cold) but I do think that it will fire right back up again with no delay when showering - When I am filling with the tub turned to full hot it goes cold and the Takagi is off, but fires right up when I do monkey with the temp valve.

I think flow issues below may be part of the problem - but not the entire reason.

Since the problem occurs, and originated, on tub filling, with the valve set all the way to hot (measured around 113F), I tend to think it is something in the Takagi - However, that being said a recent post in the bath and shower section here makes me think that it might be a shower valve and Takagi flow combination of problems...

"If you have the same problem after cleaning and flushing your valve, the other reason can be an undersized instant water heater. Thermostatic valves cannot cope well with differing pressure between hot and cold. Instant water heaters can reduce the pressure on the hot side too much for the valve if it is undersized."

If my unit is no longer flowing at the same rate as new then it might explain the sudden change in the last few months. My other concern is that it works great at a sink even with a 1gal/min low flow aerator. I do have low flow shower heads on some spots and a filter which would restrict the flow even more - but I can't imagine the flow is dropping lower than the threshold. Something to test. Also if I have fairly high water pressure (possibly 100psi plus) how much does it drop going through the Takagi and is that now part of my problem.

[Dana]

It may/may-not be related to the problem, but 100psi is pretty high! A pressure reducing valve at the input to the house can save you a lot of potential problems down the road. A high pressure studding stopping flows creates huge water-hammer pressure spikes, which takes it's toll on the plumbing over time. Solenoid operated valves in dishwashers & washing machines are typically bigger cuprits than manually operated faucets & valves, but those are by no means immune.

The TK1 is pre-set to 120F output, so with normal distriution losses and minimum mix on your tub mixer it's not surprising to see 113F. The head presented by the TK1's heat exchanger at 1.5-2.5gpm is but a tiny fraction of the 100psi- at full flow I'll bet you're still seeing over 80psi. Most will flow better than 5gpm with incoming pressures at 30psi street-pressure. The minimum operating spec for the TK1 is 15psi, max 150psi- it would have to be scaled up to near full-blockage to reduce the flow to the point of flame-out with 100psi behind it.

But if the heat exhcnager's head is creeping up over time from scale to cause sufficient pressure differential on the mixer, that's an entirely plausible explanation for the symptoms, and would explain why even a low-flow un-mixed tap doesn't have the problem. It's not that the flow though the TK1 is inherently low, but the pressure difference at the mixer causes the mixer to fluctuate or shut down the hot side. Lowering the pressure on the entire system to 30-50psi may or may-not improve the situation here, but I woudn't rule it out.

If it's a pressure differential issue it can be fudged/fixed empirically with a ball valve to throttle back flow on cold side ahead of the tub/shower mixers to better match the pressure on the hot side when the water is running.

[monty]

More tests:

Tub:
Filling the tub with the water turned all the way to hot - the water heats up and as soon as it gets hot it immediately goes cold it is pretty easy to tell it is going to happen because the water flow changes from slower with the hot to a more forceful flow due to both hot and cold coming on- check the Takagi - OFF...Turn the mixing valve from hot back to cold and then return to hot - immediately the Takagi turns on. Water is cold for a little while then warms up and finally gets hot - it runs hot for 30-40 secs then goes cold - Takagi is off again...

Shower:
My main shower has 2 shower heads in it, so it is easier to test Hot/Cold issues. I was able to switch out my suspect shower #1 with a full flow 2.5gal/min shower head - the water went cold even quicker this morning after only a minute or 2. Incidentally there is plenty of water flow and pressure at this shower. I turned on the other side - shower #2 (also with a 2.5gal/min head) and after waiting for the cold water to clear the water on that side never went cold. I couldn't check the Takagi but I assume it shut off.

The tub and the shower all use Hansgrohe Thermobalance mixers - they have worked for over 5 years with the Takagi. The Tub Themobalance Valve and thermostatic cartridge on the tub are brand new this week.

My list of checks and tests for this weekend are:

1. To check the flame-detector in the Takagi
2. To contact Hansgrohe about a new Thermostatic cartridge for shower #1
3. Buy a water pressure gauge for my water to see if I am indeed over 100psi or exactly where I am at. I may install a Pressure Regulator on the incoming water line to the house if I am above say 85psi.
4. Try to locate the Remote as recommended above

Any other things to check???

[Dana]

It's not the flame detector- you'd need to power cycle the unit to clear the error state from the controls were that the case.

I'm not sure if there's an easy way to monitor/measure the cold & hot water pressure at the mixing valves, but that would tell you with a higher degree of certainty if that were a primary factor (and I think it IS.) If the mixer is reacting to the higher temperatur as it warms up by throttling back, and the pressure difference is too high causing the hot side flow to drop below 0.6gpm for even 1 second the Takagi will (rightly) turn itself off. If/when monkeying with the mixer restores flow to the Takagi, it re-starts, as if it were a new draw. This smells right- the solution is to better balance the pressure at the mixer during flow. It may have been on the hairy edge of doing this all along, and either scale or something else on the hot water distribution path or a change in the water pressure in from the street has pushed it the half-hair over the edge.

As a further diagnositc along these lines: Run a bathroom sink's hot tap at some low flow that the TK1 can sustain without flame-out, then try running the tub/shower mixer at the same time. If the mixer can't deal properly with the hot/cold pressure differential, it may vary in temperature or turn completely cold, but the flow to the tap should keep the TK1 convinced that there's still a draw in progress and it'll stay hot.

[monty]

I tested our water pressure and in the afternoon it was 95 psi - in the morning it was over the 100 mark on the 100max gage.

I was able to install a pressure regulator on the incoming water line to the house - 45psi was too low of a flow for my liking, so I increased it to 60psi and now the shower and tub valves seem to behaving better - time will tell of course.

Is there a good pressure that people here would recommend for a house????

I am still a bit suspect of my Water Heater - but now I can do hot cold mixes much easier than before so it is possible that the problems will go away.

As an aside:
Quite an interesting thing happened during a tub fill on Friday Night before I put in the pressure regulating valve...I was using the temperature mixing valve and getting an incredible screech and hum from it when the water temperature changed - when this happened the downstairs DirecTV box & my Harmon Kardon Stereo system switched to a different channel and the volume increased to a very high volume on the receiver. I had several people over and they were very surprised it happened - so somehow the frequency hit just the right tone to vibrate the IR sensor to think it was a IR Signal??? Very Strange Indeed.

[Dana]

30-50psi is fine 60 a bit high but nothing to sweat about. Most pressure & temperature relief valves only cut in at 75psi at their lowest setting.

I'm wondering what the spec is for max operating pressure on your mixing valves(?). The spec for this one recommends 38-65psi, which would put you near the high end of the recommended range if you're running 60psi.

It's unlikely that mechanical vibe from an oscillating mixer valve some how induced a digitally encoded IR signal. Sure you weren't hit by lighting, or a car didn't knock into a power pole crossing some wires 2 transformers away, creating a power surge or voltage spike? A power disturbance could confuse the TK1's control board enough to shift the temp at the same time that other electronics were getting similarly whacked.

In any event, the running cold symptom seems pretty clearly to be a mixing valve problem, not a problem with the TK1.

[monty]

Thank you for all the help & suggestions - I will report back any problems if I have any more.

[Scott D. Plumber]

I tell You what I think might be going on. Check your gas pressure! It should coe out of you have a pressure issue but I've seen weird stuff sometimes...like this. You might need (will need) a qualified gas person to check it. You should have between 6"-10" if Natural Gas and between 9"-13" if LP with no more than a 1" pressure drop when the unit goes to high fire.

I suspect that with all this "Global Warming" going on (Sarcasm intended) that your heat is on or other gas stuff, or it just needs more gas because the incomming water is colder and is is having trouble. Another cause of this is a bad gas regulator. (Yes it happens) If the regulator can not respond fast enough to an increased gas load it can cause a temporary malfuntion on the heater.

See these things are sneaky. They'll do a "head Fake" on you sometimes and make you chase your tail.

Try that. If there is no code, its most likley not the heater! Flame rods don't heal and they don't often go bad so I don't think that's it. Flame rod would give you an error #12.

[Dana]

Wouldn't the issues with gas pressure tend to show up at the lows & highs modulation, rather than mid-fire range you'd see during showers? (I wouldn't know, not having had to chase these.)

To be sure there is plenty of under-sized gas distribution plumbing around where a tankless was swapped in when a tank heater failed.

[activa]

Hi, glad I found the forum, I'll post my problem here since it's similar and the thread's still warm.

I have a TK-Jr that heats both the radiant flooring and domestic hot water. It usually works fine (great, in fact, considering the size); however, in the mornings, after it has been working a while to heat the house, when someone tries to take a shower, the unit shuts off. The diagnostic led blinks three times. Resetting it by cycling power resolves the problem (until the next morning). The unit is inside and I don't have the controller with the diagnostic codes.

[Dana]

Hi, glad I found the forum, I'll post my problem here since it's similar and the thread's still warm.

I have a TK-Jr that heats both the radiant flooring and domestic hot water. It usually works fine (great, in fact, considering the size); however, in the mornings, after it has been working a while to heat the house, when someone tries to take a shower, the unit shuts off. The diagnostic led blinks three times. Resetting it by cycling power resolves the problem (until the next morning). The unit is inside and I don't have the controller with the diagnostic codes.

Refer to page 17 of The Manual, for the complete list of what 3 blinks might indicate. Of the 5 options indicated, most would require a competent service tech to fully diagnose and rectify. Without the exact error code you're not likely to be able to narrow it down much. Find an online deal for the RE-02 controller and install it.

If you're committed to a DIY fix, once you have the error code figured out you might try Takagi's telephone tech support, but finding a trained tech familiar with the model will likely resolve the situation more quickly (and safely).

(BTW: You may get quicker/better responses on this forum in the future if you had post your issue as a separate thread rather than jumping on an existing one. The discussions get confused very quickly when discussing multiple unique problems on different models & situations.)

[Scott D. Plumber]

Get a Manometer and know what your gas pressure is doing during all this. Could be some clues there.

[hj]

ithout trying to read everything that has already been posted, if the water is going cold it is either because the flame is not staying on, or the water is flowing through the heater too quickly to be heated properly. Have someone run the shower while you observe the heater. Hold onto the outlet pipe so you can tell the water temperature, then if it gets cool observe the flame to see if the burner is operating. High flow and a "limed" up heat exchanger would give you cool water. This assumes you do not have a recirculation system connected to the heater.