Tankless Bosch AquaStar 125b ng- water doesn't heat past lukewarm
My tankless water heater started acting up a couple of months ago and sometimes would not heat the water to warm. But in the last 2 weeks lukewarm is the hottest that it gets. Bosch is not helpful. So I have checked and cleaned the pilot....but the pilot is fine and oddly enough the burners fire but they just don't heat the water much. It is flow controlled and the knob to adjust the flow also adjusts the heat. I've noticed that even with the heat all of the way up, the pressure at the bathroom sink is exactly the same as with the heat all of the way down. So if it is flow controlled then with the heat all of the way up I should have at least a change in pressure. Considering how much it costs for replacement parts it is imperative that I figure it out before I just start replacing things. There has got to be a reason that with the burners firing it is not heating past lukewarm? There has been no change in anything in the home such as plumbing or appliances. It is a gas heater and there has been no change in how my gas furnace or range work so I'm sure it isn't related to gas. I'm stumped! Any suggestions? The only responses I seem to get are about the product itself and how people feel about that particular company which doesn't help me at all! Thanks! Let us know if you still need assistance...... Joe, did you get the 125B working up to temp? If so, let me know what you found wrong, as mine has also been experiencing a decrease in max temperature. I am on city water, and took the heat exchanger off this morning and poured white vinegar into it, letting it soak for 30 minutes. I did not see any scale, which is what I expected since the city water is good. Next, I removed and disassembled the water valve. The inline screen water filter was deteriorated, leaving only the plastic frame. Examining the water valve, I found only a bit of corrosion on the upper pin. What I did find was a small pebble lodged in the venturi, which would normally have been caught by the screen filter. Upon reassembly, I found that the flame height is only about 2 at max heat and water flow, whereas it had been only about 1.5 with the pebble clogging the venturi. The burner will not come on until a flow rate of one quart in 20 seconds in reached. The specs say it should come on at the lower rate on one quart in 30 seconds. The water at full flow seems to be getting somewhat hotter, but not enough to scald anyone. It appears to me that the water valve is designed to increase the gas flow at full water demand. The ground temperature of the water here in winter is about 50 degrees F. Does anyone know what the flame height should be in these natural gas tankless water heaters? The Bosch 125B is rated at 117,000 Btu max. Chuck Now, after a couple of days of use after taking the pebble out of the water valve venturi and lubricating the push rod, my Bosch Aquastar 125B is working good again. I think that if anyone has fluctuating temperatures out of their tankless water heater, it would be good to have a look at the water valve. My instruction manual states that the water valve needs to be cleaned and lubricated every two years, and the water valve possibly replaced every five years. My heater has been in continuous use for 10-12 years now, and I finally had a problem. The water valve is easy to clean and lubricate. However, to get a hotter stream of water in a quicker manner in winter, I am going to install a small 7 gallon Ariston 120v electric water heater immediately downstream from my Aquastar. My tankless heater will feed water directly into the electric heater. My goal is hotter water, more quickly. What do you propose that 7 gallon wh is going to do for you? You are feeding it hot water, so it will never come on. By the time the demand is made, it won't make any difference because the tankless will have ignited. Ever thought about a recirculator?? The tank acts as a buffer so you don't get the sandwich effect. The electric is no hooked up.... One of the drawbacks of tankless heaters is that there is a delay in the hot water getting to the point of use, which is caused by the time it takes for the tankless heater to heat up the heat exchanger. The small tank heater will get heated water from the tankless heater, and heat it further. Mostly though, it will sit there with a 7 gallon capacity of hot water ready to go directly to a faucet, which will result in having hot water much faster. In addition, with the two paired together, I keep my endless supply intact. The Ariston will be hooked up to a 120v source. I will be hooking up the system today and will let you all know if it lives up to my expectations. Chuck I am happy to report that the addition of the 7-gallon Ariston electric tank downstream of the Bosch Aquastar 125B met all of my expectations. I now get hot water in half the time, and it is much hotter. I wish that I had done this 10 years ago. The entire installation of the Ariston took me 8 hours, which included parts shopping, fitting copper tubing, electrical connection, etc. I put the Ariston on the wall directly below the Bosch, keeping the new tank off the floor about 10 inches to make it easy to sweep under. My mistake was putting it a little too close to the bottom of the Bosch, which caused some interference between the new tank lines and the Bosch water valve. The Bosch Aquastar 125 series is a fine unit, but it has a limited flow-through capacity, making it useful for only one faucet at a time, especially in winter when the ground water is cold. Most people would spend $1,000.00-$1,600.00 for a larger tankless heater to get greater capacity. I spent about $240.00 for the Ariston tank and needed fittings, getting hotter water in the process. Having both units creates an ideal combination, IMHO. I also wondered where to easily get a new inline water filter for my Bosch, since the old one had completely fallen apart. I looked at inline screens at the store and saw a packet of 3 SS screens that are usually placed into the end of a garden hose. The cost was $1.49, so I took a chance. One of the new screens with rubber surround fit right on the end of the water valve inlet, and the Bosch nut went right over and sealed down tight. End of search, and I have 2 extras. Happy plumbing, Chuck I think that all tankless water heaters have some sort of gas control valve that is water flow actuated. My Bosch Aquastar 125 is designed in that manner. The control valve has a diaphragm inside that moves under water pressure and flow, opening up the gas as more water flows through the valve. My problem is that there was a small pebble in the control valve venturi, with the result that the diaphragm would not rise enough. The water was lukewarm. In addition to examining the gas control valve for an obstruction in the water flow, you may also want to boil out the heat exchanger with a 50/50 solution of white vinegar and water. If you are on well water, minerals will build up in the heat exchanger, but they can be removed by boiling. The Bosch site suggests removing and boiling out the heat exchanger every couple of years if there are minerals in your water. Since I am on city water, my heat exchanger was clean after 10 years of use. As far as quantity of hot water through the unit, there is an upper limit due to overall design of the tankless heater. The heater itself does not regulate the quantity of water flow. What is regulated is the gas flow to the burner. It will not come on until the heater detects water flow through the gas control valve. The more water flow, the greater the diaphragm movement and the more gas and heat goes to the heat exchanger. Hope that this assists others in getting their tankless heaters working again. Regards, Chuck
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