Unlimited hot water

[schweizer]

I can address a lot of the questions from experience in our house:

We have a Bosch propane on-demand water heater in our new house, 1.5 years old. It works great! We love it. In the first 6 months our propane use was only about 60 gallons, but we are off-the-grid and have a large propane stove/oven, gas clothes dryer, and backup propane forced-air heat, too. That seems to be great efficiency, with a 2700 sq ft house, 2 adults, 2 kids.

( One thing that probably helped our efficiency a lot is that I preheat the water first with the water coils in the woodstove which go to a heat exchanger in a 500 gallon holding tank under the house. The water in that 500 gallon tank then acts as a heat reserve to preheat water coming from the well (maybe 45 deg in winter). My goal is to feed the on-demand heater with nearly 100 deg preheated water so it only has to heat the last 20 degrees. Our experience shows that if we use water that is preheated close to the 120 deg set point of the water heater, it may cycle on/off or not start up at all. )

I haven't done the vinegar treatment to the Bosch yet, but it will be fairly easy because of the valves under the heater that the OP mentioned. We do have very hard water, and have a salt-free water softener which seems to work great for mineral deposits on the faucets.

On our heater, the air intake and exhaust are the same metal pipe -- it's a pipe within a pipe. The inner pipe is exhaust and outer is intake. The exhaust gas is quite cool because of the counter-current heat exchange principle.

Marcus

Edit: Also, we have not experienced much of the hot-cold-hot sandwich that many people worry about. All the pipes in our house are copper, so it takes a little longer to get the hot water to the right temp, but the heat stored in the metal pipes tempers the cold water that comes in-between from turning the hot water back on again.

 

[Allee]

We installed a Bosch hot water heater in our new 2 story home in the country about 7 yrs ago. We're on a well and have propane. Our initial problem with the unit was that it took forever for the water to warm up and when we tried to adjust the temp it would shut down. When I called a local (60 miles round trip) service rep listed by the company, he seemed to know little about our unit and the visit was a waste of his time and ours. I then called the company and was directed to remove the front panel and reverse a couple of wire clips on some copper tubing (why didn't the service rep know this?). We've had hot water ever since but have to run the water, and well pump, several minutes before it turns hot. Then it's too hot and if we turn it down too far it will go cold and needs to be reset. In washing dishes and clothes we again don't always know if it's cold or hot unless we check. My wife wants to pull the unit and have a tank installed but then we're out $1,000.00 +/- on our initial investment. Wish we had "hot water on demand". Has anyone had similar problems with the Bosch, Aqua Star? Any opinions or solutions?

 

[charlz]

If you want to pre-heat the water why not install a wild loop with a small circulater as I did. Then you always have hot water as soon as you turn on the faucet and the tank gets the advantage of the warmer water returning to it instead of 40 degree water.

Are you refering to those systems where you put a 'bypass' at the faucets and run a recirc pump so you always have hot water at the facets?

 

[aczlan]

What model do you have?

Aaron Z

 

[Allee]

Pre-heating the water! What a grand idea. Wish we could do the same. Running hot water to our second story is a waste of alot of water and then the unit will sometimes shut down mid-shower. We have also found it to our advantage to leave the water running somewhere when we go to the garage to reset the unit. Wish we had shopped around and checked the consumer guides before we made our purchase.

 

[Allee]

I've heard of that before but know little about plumbing and of what it would take to revamp my unit. Warming the water before it gets to my heater sounds like the way to go. Is there a tech report I can refer to for all of the details and supplies?

 

[Allee]

AQ 250 SX LP is my model number.

 

[Allee]

AQ 250 SX LP

 

[aczlan]

AQ 250 SX LP is my model number.

There is a manual for your unit at http://www.houseneeds.com/shop/manuals/bosch_250sxmanual.pdf
I would check the troubleshooting steps on pages 24-25.
Is there an error message that shows up when it shuts down?
Your symptoms sound like you may be getting a A9 error which is "Temperature limiter opened circuit (overheat)" form the burner not throttling down when the water flow goes down.

Thanks

Aaron Z

 

[Allee]

What model do you have?

Aaron Z

AQ 250 SX LP

 

[PineRidge]

Are you refering to those systems where you put a 'bypass' at the faucets and run a recirc pump so you always have hot water at the facets?

See this


My system uses a dedicated return from the furthest faucet and a pump to keep hot water circulating at specific times of the day.

 

[schweizer]

Ooops, I was wrong. We have a Rheem water heater. Model #: RTG-84DVP

 

[Allee]

I try to locate my owners manual. Thanks

 

[aczlan]

I try to locate my owners manual. Thanks

The link I posted earlier ( http://www.houseneeds.com/shop/manuals/bosch_250sxmanual.pdf ) has the owners manual for your unit.

Aaron Z

 

[Allee]

I found the owners manual but it looks like I need to find a confident tecnician to work on the adjustments. I don't have a CO2 meter nor would I know how to read it. I may succeed in getting our temperature stabilized after all. Any clue on how to contact a tech for the Aqua Star. I'll probably have to get on the horn and find one. Thanks for the help.

 

[aczlan]

I would start with the following:
1. Does it throw a code when it shuts off? If so, what is the code?
2. Watch the water pressure while someone is running water and see if it changes appreciably
3. Get a non-contact thermometer (such as Infrared Thermometer - Non-contact, Digital Thermometer ) and monitor the temperature of the output pipe.

The section I was referring you to:

HOT WATER TEMPERATURE FLUCTUATES /UNIT DEACTIVATED
• Unbalanced pressure in water lines Any restriction caused by the water heater in the hot water system can result in uneven pressures between the cold and the hot. In such cases when mixing cold water at the tap (manually or automatically through a mix-type shower valve) the lower hot water pressure may be overpowered by the higher cold water pressure in the building and cause the hot water flow rate to fall below the minimum rate required. A pressure balance valve will help to resolve this symptom.
• Temperature balance valves If the outlet water temperature is set too high, the heater can produce temperatures that are too hot. A temperature balance shower valve can automatically mix in cold water to reduce such hot water temperature. In the event of any temperature instability with the use of a temperature balance shower valve, refer to shower valve manufacturer's instructions for internal adjustment setting. Adjustments should be made to the hottest setting in the shower valve. Additionally the temperature control of the heater can be lowered to produce a more comfortable hot water temperature.
• Inlet water pressure is erratic due to fluctuating supply water pressure For installation on a private well system with the use of a pressure tank, the lowest pressure range setting
recommended is 30-50 psi (2.07-3.45 bar). The use of a pressure reducing valve after the pressure tank is also an effective way to maintain a constant water pressure to the water heater. Watts brand 25AUB-¾” or N35B-¾” pressure relief valves or equivalent are suggested.

Watching the system pressure and output temperature (along with looking on page 26 tor what the codes mean) should give you an idea what is happening and let you know if the tech is feeding you a line of BS.

Aaron Z

 

[Bikewanderer]

Up north here they work ok when the water inlet temp is 45ｰ or higher but on municipal water we get water temps in the range of 36ｰ from early in December on through the winter. The last time I looked at these when I replaced my water heater 7 or 8 years ago there was no readily available model that could handle a 2.5 gpm shower head at a 100ｰ rise.
Looking at the American data sheet in the OP it seems the biggest model (540) can give about 3.6 gpm at 100ｰ rise, although you are still not guaranteed an acceptable result because of inefficiencies that can creep in with pressure drop, scale buildup and an insufficient propane supply which cannot make vapor fast enough in the coldest temps to support a 199,000 btu burner. So if you're in the northern tier or northeast do your homework, know the coldest water inlet temp to expect, know the vapor capacity of your propane storage at the coldest temps your area experiences and know the scale tendencies or hardness of your water.


Ray

This has also kept me from doing it. 3.6 gpm isn't enough to wash dishes or the laundry and shower at the same time, so why bother? I have six people at home and soon to be a seventh. Our bathtubs are busy all morning and our water heater can barely keep up, but this would be worse than what I have now.

I don't think 200k btu will affect vaporiation rate too much unless it's a constant draw. I pulled 2.5M BTU off our 2000 gallon tank at work all day a few weeks ago and it never lost a lot of pressure. If it were a constant draw in cold weather on a low tank you MIGHT have issues.

 

[tkappeler]

See this


My system uses a dedicated return from the furthest faucet and a pump to keep hot water circulating at specific times of the day.

I have thought about this kind of re-circulating solution, however; I am going to use PEX and a manifold to distribute to the end points. There is no way to effectively recirc. Even if I create a loop for recirc off the manifold, I would only keep the line from the HWH to the manifold hot, all of the other lines are still cold.

 

[Bob77064]

That loop is a great idea, I wish we had one.

 

[WayneB]

I installed a Bosch FX 125 at our place in the mountains several years ago and we have enjoyed it. Key reason back then was for the ease of winterizing and with the old 40 gallon tank from time to time I would forget to turn it off and we would be gone for two weeks and heating hot water for no reason. With the on demand no problems what so ever. The real plus was getting to camp late at night and having hot water instantly. Also one could take a shower for as long as they wish and never run out of hot water.

We also have a larger Bosch On Demand Heater at home and really like it here too. The newer controllers are proportional and we have not had any problems in cold weather with the unit. I have kept propane records and we are averaging around $12.00 a month for hot water. I am using 100 pound tanks and have to haul them to get filled, but the price is cheaper than deliver cost so I continue doing it. Our primary source of heat is wood and we have hot water oil furnace backup but it is turned off and only used if we are going to be away for an extended period of time.