Hi, we have new Buderus ST120 32Gallon 155 GPH hot water maker installed because our plumber told us that we will never run out of hot water and we can do multiple things at the same time, if we use this.

However, it has been nightmare. We take baths everyday and the hot water only fills upto 70% of the tub and then turns lukewarm or cold. This happens, even after we do not use water at all for more than 8 hours.

We are never able to do two things like running washer or dishawasher at the same time.

Our plumber brought Buderus supplier and tried to resolve the issue but it became worse. It seems that he even reduced the volume of the water, although he claims that he didn't, in order to slow down the water, so that the water maker can catch up. However, even this very inconvenient solution does not work. It still does not fill up the tub with hot water.

Now, he is saying that it is normal NOT to fill up the tub like this. If any of you used THIS Buderus water maker, please let me know whether this is normal. Thanks in advance.

Yes, I have used that domestic water tank, and yes, it will fill a tub.

There are a million questions we could ask you here, to try and determine what the problem is. You need to find another Buderus guy.

Could be a control problem, boiler problem, piping problem, how big is the tub, where are the pipes, and on and on, etc. etc.

One thing it will NOT do is accomodate more than one load at a time, unless the plumbing in the house has been changed. The boiler and tank can make the water, but the pipes in the house may not be big enough to get the water throughout the house. If you could run laundry and the dishwasher at the same time before, you should be able to do this now.

I've been to houses where they can run five showers, all at the same time. BUT, the plumbing was designed and installed for this from the start.

You need a different guy. There is a find a contractor feature on this site.

32 gallons of hot water will not fill a tub by itself.

the boiler must get involved.

if you keep running a tub, does the water warm back up eventually, or does it stay cold?

one thing you can try, if you have a 3-way tempering valve between you and the tank is turning up the temp of the indirect. This will increase your storage temperature and turn on your boiler earlier as well during a heat demand.

but if your tub is very big, it may not have the horsepower to do this. how big is the tub, and what model boiler do you have on this tank?

Guys, Thanks for replying.

Jonas, I am searching for another plumber but it is not easy to find knowledgeable person because of my system. I actually found our plumber's info from the contractor list you mentioned. I wonder whether I can report the issues we had with this plumber to RPA because we had so many problems...

NRT.Rob, My tub's capacity is only 41 gallons.I have new Buderus GB 142 24 also installed, because I also have radiant heating system, which we have not used much and do not use nowadays. I am afraid to use it in the future and find problems with that, too.

Our plumber told me that it is indirect water heater so it will NOT be affected, while we use radiant heating, when I was worried that we will have worse problem while we use radiant heating. If the boiler is also involved with water maker, isn't the radiant heating supposed to affect hot water system?

Our plumber also decreased the temperature of the hot water from either boiler or water maker so the hot water from the tub spout is not that hot-less than 120 degree- because he thought that it could resolve the problem, which did not work, either.

This message has been edited. Last edited by: JSL,

the boiler can do what is called "domestic priority", which means when the domestic calls for heat, it stops doing heating and does only domestic for awhile. this is for a short enough period of time that people typically don't notice.

Typically you want about 110 at the fixture, a storage temp of about 140, and a tempering valve to limit the outgoing to whatever you need to hit 110 at the fixture. Also be aware that 155 GPH is only about 2.5 GPM.. that's about the demand of a single regular showerhead, though I would expect you to be able to do that continuously, with slightly higher demands for shorter periods of time. So if this tub fill is something like 5 GPM or some other fast type fill, it wouldn't be hard for you to outstrip the boiler.

That's a pretty small demand overall though, so something is definitely up.

-it may be that the boiler is not running to high temp on a domestic demand and therefor is not exchanging heat fast enough. If you start a DHW demand and look at the boiler, it should tell you the temp of the water coming out. It should rise steadily towards a max of a fairly high number, like 160+ deg F.

-It may be that you do not have the 3-way valve, and so your tank temperature itself is too low and the boiler can't keep up on its own. You should be able to see if the hot out of the tank goes through a 3 way valve on the way to your fixtures. If not, then turning up the tank temperature too much risks burns.

You should be able to get some combination of storage temp and outlet temp to get this tub to fill unless something really weird is happing like the tank is plumbed in upside down or something.

I would agree to check the items already mantioned.
I would also check the pump size. If it is a Grundfos 15-58 three speed, make sure it's on speed three,as I recall. That's the match for that size boiler and indirect, when there is a call for DHW the pump needs to overcome the head thru the boiler and tank. A 26-99 pump would be better.
Also check the pipe size from boiler to tank. Even though the S120 has 3/4" supply and return tappings, the boiler has 1". Run 1" all the way to the tank.

Last, a standard 5' can tub hold more the 150 gals. of water. Every cubic ft = 7.48 . The s120 may be a little undersized.

quote:

Originally posted by JSL:
Hi, we have new Buderus ST120 32Gallon 155 GPH hot water maker installed because our plumber told us that we will never run out of hot water

Seems like too strong statement for a 32 gal tank.

I'm not a plumber, just a regular homeowner. But here is "my 5 cents". (I assume we are talking about indirect water heater.)

I have a 40 gal indirect and it can fill a tub. It even can fill a tub for my wife while I'm taking a shower in another bathroom.

However, when I fill our small jacuzzi, it runs out of hot water. The jacuzzi is about twice a size of the normal tub.

So, I would say 32 gal is not much but should definitely be enough for a tub.

I would start from checking the temperatures:
- what temperature the aquastat is set to?
- what's the supply temperature?
- what's the return temperature?

The aquastat should be set in 130-150 F range (higher, if you are using mixing valve)

The supply temperature should be 30-40 F higher then the aquastat setting. (higher means greater output and lower efficiency)

PS. What kind of boiler do you have?

whoa tarp, you don't want an indirect over 150.. gets pretty hard to satisfy at very high temps.

you kind of contradict yourself there a bit, careful now

Sorry, guys. Because I am not knowledgeable with plumbing, it was difficult to check things out... I have attached the pictures so would you guys please take a look and let me know whether the 3-way valve has been installed and pipe size is right..etc? Please feel free to let me know if you need additional pictures to see.

Meanwhile, I will ask him about the boiler running temperature setting during domestic demand.

In terms of the pump, it is Taco, not Grundfos. My plumber told me that he changed the pump, telling me that the pump was defective. After it did not resolve the problem, he told me that he changed the temperature sensor in the boiler but it still does not work...

2nd Picture.

Last Picture.

Thanks for the pictures.

From the looks of it, the dhw pump is a 007.
That pump has a 0-20 GPM and 0-11 ft head range.

In order to meet the specs of the boiler and tank combined on priority a larger pump needed.

you do have a 3-way tempering valve installed there, that is good.

I appreciate everyone for replying. Finally, I feel that this might be resolved. I talked to my plumber about pump size and boiler temperature. Buderus suggested to change the pump to Grundfos and also change the aquastat.

We were very frustrated because both our plumber and Buderus supplier recently told us that it is normal not to fill a 41 gallons tub and we should not expect to do multiple things at the same time, as if we were expecting too much. They blamed on our tub capacity and our habits. Now, it seems that they listen to me because I told my plumber that others also think that this is not right. I will wait and see how this goes. They will work on this next week and I will report back. Please let me know if there is anything else that my plumber should check. Thanks again.

to maximize what you have, I would suggest a storage tank temp of 140, a boiler domestic max temp of 180. use the 3 way to set your outgoing temp to 110 to 120 depending on what temp that gives you at the fixture.. you don't want it too high.

Hopefully that plus the pump switch will do the job you need it to do! If not, upsizing the storage tank can solve it.