Sunday, July 20, 2008

Thanks for Tank and Tankless Heaters

Last weekend, Jim and I finished making the final connections for our tankless water heater. I was admittedly nervous since this is a used Takagi TK2 tankless water heater we had gotten off of Craigslist. So rather than just cutting out the old tank model, we installed a shut-off isolation valve on our old water heater and left it in place for now. That way, just in case we run into problems with the tankless and need to revert back, it's a simple switch.

Jim GillSo, once the new equipment was in place and water lines were soldered together and leak free, we flipped the switch on the tankless water heater. Water flowed in and no leaks! I turned on a hot water tap, and water began to flow through the tankless. Once the flow was high enough (more than 0.5 gallons per minute), the electronic igniter lit the flames, which we could see through a tiny window (Jim is pointing to it the photo). Then the exhaust fan kicked on to push the fumes out the special stainless steel venting. Shortly, there was hot water flowing through the tap! Yay!

In a tankless water heater system, the hot water takes a bit longer to reach the taps than a regular water heater would. This happens because there is no constant heat source heating water all the time, and no standby heat is transferred to the water pipes. This is a trade-off with a tankless water heater. Less fuel is needed to heat, but more water is used and wasted down the drain as you wait for the hot water. Fortunately almost all of our plumbing runs are relatively short, so we haven't noticed this isn't a big deal. It takes maybe an extra 20 seconds at our furthest plumbing fixture.

Anyway, we've now been living with the new tankless for a week. Sunday night, Jen was very happy to finally be able fill the bath tub with hot water instead of running out halfway through! But we noticed when taking a shower that the hot water fluctuated off for about two minutes (completely, so it was cold!) and then came back on.

Takagi TK2 Flame Sensor, Igniter, and BurnerI read the TK2 manual, did a bit of research, and found a great discussion on problems with Takagi TK2 water heaters. This gave me some good ideas such as cleaning water inlet filter, cleaning the igniter and flame sensor (next to the tiny burner window) as well as checking the temperature sensors in the water intake and outtake lines for any clogs. So I did all this. At first, looking at this thing with the cover off is quite intimidating, but if you try to look past all the electronic wires, it's relatively straightforward.

However, after all these maintenance tweaks, it seems we still have occasional problems with the shower. We still get hot water there (and everywhere else for that matter), and there is no problem if the shower is set to full-hot (not mixing with cold water). I wonder if this is mixing valve issue so we'll have to do a bit more investigation on the temperature fluctuations (and maybe even call Takagi) to get this figured out.

Anyhow, despite these initial problems, I'm quite pleased with the fact that the system works, and I'm really looking forward to cutting out the old tank-style water heater and getting some extra space in the small utility room / shop area in our basement. But we'll hold off on that until these issues are resolved, knowing that if needed, we can fire up the old beastly water heater at any time.


Michael said...

You might want to make sure your two minute cold water patch isn't coordinating with a toilet flush, a dish washer, or a clothing washing machine. In that case your shower needs a modern mixing valve that adjusts to changes in water pressures.

jay said...

Thanks for the tip Michael. Our shower valve is fancy new Moen Positemp mixing valve. I contacted Moen about this issue on a Sunday afternoon and received instructions by Sunday evening on how to take out, disassemble and clean the valve. After doing this (and cleaning the showerhead too), things have evened out and we don't seem to be having this problem anymore.

mauro said...

being born and raised in another country (brasil) and traveling to europe constantly (for work), I have a slight different approach to this. We have been using tankless in brasil forever (unless the house doesn't have central water heating, which happens a lot, and in that case, the showerhead has a resistance built-in that heats the water once you turn the water on - electric. Sounds dangerous, but I haven't heard of anybody dying from it) - anyway, we don't mix the cold water with the hot - we can, we just don't. We put the water temperature in a way that it's comfortable for a shower, and only turn on the hot water. This way, you don't "extra" heat the water just to mix it down with cold water to "cool it down" a little - which is necessary with a regular heater - you need the water extra hot so you have enough for your shower. With the new tankless heaters, that's even better, since you can put a remote in the bathroom, and choose your temperature. You only heat what you use, and never overheat. This way the pressure is 100% at the tankless heater (because you have the hot water knob all the way up, and the cold off) and change the temperature AT THE HEATER. Does that make sense? Also, there's a way for you to loop the water that is cold back to the tank (again, that's fine, because if you're using cold water only, you get it right away - if you want hot water, you only turn on the hot water faucet, and it will start once the hot water is there - no wasted water) - or you can put those smaller hot water heaters near the faucets to get instant hot water - they heat the water in a split second, and once the hot water from the main tankless reach the faucet, it turns the small heater off. Just a few thoughts. But NOT MIXING cold water is the way to go - the way the tankless was intended to operate. It's hard to get used to it since you've been mixing hot and cold your whole life, but trust me on this. And you're saving money, and resources.

Bill said...

This cold water problem happens when the flow is not high enough to keep the flow sensor on so the heater shuts down. An easy test is to turn on an additional hot water appliance to increase the flow rate and verify the heater then stays on. A low flow showerhead, pluggled showerhead or partially plugged heater filter can cause this.

Mike said...

Thanks for all the info here. Especially your helpful picture, Jay! This isn't even in the manual.
Mauro, I would be interested to find out how the cold water is recycled in Brazil, since we waste so much water waiting for it to get hot now.

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