We had one of those installed by a plumber last fall. I forget the model numbers, but its a 125 something-or-another, and its the one that requires no standing pilot and no electricity, it lights the pilot by a small generator activated by the flow of water.
But anyway, we had a problem not unlike yours. The minimum flow rate required to activate the unit was a bit on the high side, around 1 -
1.2 GPM, but the bigger problem was that temp rise was not constant with water flow. Temp rise actually increased with increased water flow. (I actually spent an hour one night at the basement sink timing how long it took to fill a bucket of water and measuring the temp, and I did that for a wide range of water flow rates.) The effect was that when I took a shower in the morning, it wouldn't reliably turn on the heater, and would usually go cold on me in the middle of a shower. A new higher flow shower head solved the problem of going cold, however I discovered that I needed to turn on the tub at the same time (tub and shower have separate controls) to get the water flow up enough for it to heat the water enough. I was getting only about 50 degree F temp rise at 1.2 GPM or so, but at 2 - 2.5 GMP temp rise went up to about 75 degrees F, which gave me a good hot shower. Of course, its not supposed to work this way, its supposed to be 75 degree temp rise regardless of flow rate, but that's how our unit performed.
We did all the usual service things they suggested (which it didn't need because it was brand new) with no effect, so we called the 800 number. First try with the 800 number got me a doofus who didn't know squat about anything, and told me I needed to be standing next to the water heater with a phone in my hand so they could walk we through some items to test. And this is with me calling from work, so I would have to go home, and besides I don't have a cell phone or cordless phone, so I would have had to wire up a phone just to try out whatever it was they wanted me to do.
So I waited a day and called back again, and randomly got a different person who actually knew what they were doing. After about 2 seconds of explanation, they told me I definitely got a defective unit, and they will send out a new one right away. (With a deposit on my credit card that would be refunded when the old unit was returned. )
Our plumber installed the new unit, and it functions better than the old one, however there is still about a range of about 10 - 15 degrees F temperature rise variation depending on the water flow. Its not perfect, but it appears to be acceptable for our use.
We got this water heater on the recommendation of another person whose unit appears to work flawlessly, however, we know yet another couple who has one of the same units that was sinilarly defective and needed a factory replacement.
My suggestion to you would be to make a few measurements about minimum flow rate required to trigger the heater (measure accurately with a marked bucket and a watch with second hand), and then call the 800 number. (And cross your fingers you get someone who knows what they are talking about.) Maybe they will allow you to try Russian roulette and give you another unit to see if that one works acceptably. It sounds to me lilke they let the consumer do the quality assurance testing in their home rather than doing it at the factory.
I don't know if it's tough to find data on the dispenser idea, but it seems like it would save a lot of energy, considering the volume that must flow through a water heater when the pipes have gone cold.
Unfortunately, this is normal operation for most tankless gas water heaters. You've got to balance the flow rate and the selected temperature. You may get some respite by trying to adjust either the flow rate or the temperature, but be prepared for sudden changes. It gets worse when someone else uses water -- opens a tap or flushes a toilet.
In the U.S. tankless gas hot water heaters are a novelty -- overseas they are considered a low-end appliance, and the better quality residences have hot water tanks. I suffered through too many sudden-hot / sudden-cold showers overseas to ever install one in my house in the U.S.
A cynic has said that a tankless hot water heater will provide you with the two happiest days of your life -- the day you first have the state-of-the-art unit installed, and the day you get the %#@&* thing replaced with a hot water tank.
My parents had a tankless system on an oil burner for 35 years. That is what was used 50 years ago. The original worked ok but when it finally went bad the replacement was trash. They loved the water heater that replace it.
A simple way of operation is turning water on full , I have water volume reducers on all spigots. My Ng savings are based on this. I agree 1/2 gpm or so may not trigger it to fire, it is just the way they operate and something you must adjust to.
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.