Problems With Rheem Tankless Hot Water Heater Configuration?

 
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Old 05-08-2008, 03:34 PM   #1
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Problems With Rheem Tankless Hot Water Heater Configuration?


We are the GC on a house that we installed 4 Rheem commercial grade tankless hot water heaters. Three of the units are hooked in parallel to service one side of the house. This side of the house has Kohler DTV shower system that can pull 15 GPM on max load which is the reason for all the tankless heaters. Additionally, we have 1 unit that services another side of the house running by itself.

The side of the house that has 3 units runs great if you create enough demand for it - demand being at least 2 fixtures running. If we turn the faucet on (2 gpm per minute on our tests) the tankless system will not engage. If we turned on a second faucet, the tankless system will engage. Rheem says the demand much be at least .66 gpm to engage the tankless units which we are far exceededing. The tankless system runs great and can easily handle all the demand of the house. The single unit on the other side of the does not have this problem at all.

Anyone everyrun into a problem like this? I have talked to Rheem, but they are not much help.
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Old 05-08-2008, 03:47 PM   #2
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Re: Problems With Rheem Tankless Hot Water Heater Configuration?


We ran into a smilar problem here. we were told to install a recirc line to the last fixture on the branch worked great for 1 month then the contractor started having a problem with the tankless not meeting the demand. the final out come was a storage tank with a recirc line no problem for 6 months now however only time will tell.

not much help
good luck

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Old 05-08-2008, 04:08 PM   #3
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Re: Problems With Rheem Tankless Hot Water Heater Configuration?


2 gpm divided by 3 units in parallel = .66gpm per unit. You are not "far exceeding" the minimum required flow rate but rather you are right at the minimum required flow rate.
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Old 05-08-2008, 04:09 PM   #4
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Re: Problems With Rheem Tankless Hot Water Heater Configuration?


How did you determine that you had a 2 gpm flow rate?
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Old 05-08-2008, 04:12 PM   #5
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Re: Problems With Rheem Tankless Hot Water Heater Configuration?


Quote:
Originally Posted by smellslike$tome View Post
How did you determine that you had a 2 gpm flow rate?
Lav faucets have a 2 GPM flow restrictor on them.
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Old 05-08-2008, 04:15 PM   #6
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Re: Problems With Rheem Tankless Hot Water Heater Configuration?


Quote:
Originally Posted by KesslerDweller View Post
We are the GC on a house that we installed 4 Rheem commercial grade tankless hot water heaters. Three of the units are hooked in parallel to service one side of the house. This side of the house has Kohler DTV shower system that can pull 15 GPM on max load which is the reason for all the tankless heaters. Additionally, we have 1 unit that services another side of the house running by itself.

The side of the house that has 3 units runs great if you create enough demand for it - demand being at least 2 fixtures running. If we turn the faucet on (2 gpm per minute on our tests) the tankless system will not engage. If we turned on a second faucet, the tankless system will engage. Rheem says the demand much be at least .66 gpm to engage the tankless units which we are far exceededing. The tankless system runs great and can easily handle all the demand of the house. The single unit on the other side of the does not have this problem at all.

Anyone everyrun into a problem like this? I have talked to Rheem, but they are not much help.
Why were these not installed in paralell and have a controller that operates on flow rate? The multi unit ones I have installed made by Takagi were installed that way per the manufacturers instructions.
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Old 05-08-2008, 04:28 PM   #7
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Re: Problems With Rheem Tankless Hot Water Heater Configuration?


Quote:
Originally Posted by KillerToiletSpi View Post
Lav faucets have a 2 GPM flow restrictor on them.
Yes, but this does not necessarily mean that if you open the hot side of a lav faucet that you get the full 2 gpm especially on a single lever.
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Old 05-08-2008, 04:30 PM   #8
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Re: Problems With Rheem Tankless Hot Water Heater Configuration?


On multiple Rinnai units I have installed at a bed and breakfast, Rinnai supplies a special wiring harness for proper operation.
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Old 05-08-2008, 04:37 PM   #9
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Re: Problems With Rheem Tankless Hot Water Heater Configuration?


I turned the hot water (only) on and put a bucket underneath to catch the water - that is how I measured the GPM.

We are using a MIC-180 controller for the 3 tankless units which is a requirement once you get over 2 tankless units.

@smellslike$tome - Rheem told me that it was total demand of .66 gpm was required, but now that you point it out perhaps it is 2gallons divided by 3 units. The way I was explained it works by Rheem is that one unit fires on until demand exceeds it and then the MIC-180 fires on another unit and so on.

Thanks for everyone's input - keep it coming!
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Old 05-08-2008, 04:45 PM   #10
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Re: Problems With Rheem Tankless Hot Water Heater Configuration?


I would go back on Rheem on this one and demand they get their field rep to come take a look. If you have to exceed .66gpm on all units before even one will kick on, then I think they have a problem in their logic circuit.

I'm sorry I don't much about the Rheem units.
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Old 05-08-2008, 04:46 PM   #11
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Re: Problems With Rheem Tankless Hot Water Heater Configuration?


Quote:
Originally Posted by gmp View Post
On multiple Rinnai units I have installed at a bed and breakfast, Rinnai supplies a special wiring harness for proper operation.
So does the Takagi, it has a built in flow sensor.
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Old 05-08-2008, 09:40 PM   #12
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Re: Problems With Rheem Tankless Hot Water Heater Configuration?


I have not installed Rheem tankless although I like their tanked wh. I have been told but do not know if it is true or not, that Rheem is manufactured by Takagi.
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Old 05-08-2008, 10:54 PM   #13
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Re: Problems With Rheem Tankless Hot Water Heater Configuration?


Quote:
Originally Posted by smellslike$tome View Post
I have not installed Rheem tankless although I like their tanked wh. I have been told but do not know if it is true or not, that Rheem is manufactured by Takagi.
Takagi is now on its own. For the past 5 or so years Noritz licensed out their technology to Takagi. Takagi was having ALOT of problems with their own designs so they made a deal. Basically it was a stripped down Noritz for the same money. Now, Takagi makes their own units, but they
(at least 07 -08 mdl's) are no where near a Noritz...IMHO.

As for this setup for the OP.....I hate Rheem tankless. What a waste of money. 3 units in parallel requires a very good understanding of EXACTLY how the systems work. The plumber obviously didn't. IF...again IF there is no data connecting cable daisy chaied to these units, well....that is just poor planning. I dunno if the units you used are capable of multi unit operating but I think it should be. Most manu's make them for that. Gotta buy a $30 cable and know how to hook them up.

Minimum demand, Noritz are .5GPM min flow to activate. .6 isn't much of a difference...but a difference none the less.

The simple fix is to data connect.

What are the MDL numbers of the units installed?
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Old 05-09-2008, 12:01 AM   #14
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Re: Problems With Rheem Tankless Hot Water Heater Configuration?


Quote:
Originally Posted by KesslerDweller View Post
I turned the hot water (only) on and put a bucket underneath to catch the water - that is how I measured the GPM.

We are using a MIC-180 controller for the 3 tankless units which is a requirement once you get over 2 tankless units.

@smellslike$tome - Rheem told me that it was total demand of .66 gpm was required, but now that you point it out perhaps it is 2gallons divided by 3 units. The way I was explained it works by Rheem is that one unit fires on until demand exceeds it and then the MIC-180 fires on another unit and so on.

Thanks for everyone's input - keep it coming!

LOL...that's a funny way to measure GPM's...

Ok, so you have GT-199's installed. They are equivalent to a basic water heater. They are NOT a "commercial" units. Rheem couldn't build a real commercial unit if their lives depended on it. The "heavy duty" units you have spec out fatter than the standard Noritz and Takagi.
I just read the manual on your units....man, I'm glad I don't install them. For the money, there really is much better out on the market. Either way...they are installed and I assume paid for, so you have the 180 controller, you need to have them interconnected. PT# is MIC-K-16. You will need 3, I saw them online for 50-80 bucks. The units all come with a standard wired remote. 2 of them are now your personal extras....you should not be using them. The one remote you have should be wired to the MIC-180, than from that manifold controller you will daisychain the 3 heaters.

Your plumber must make sure tempertures are set correctly and that the internal dip switches match. I hate dip switches on tankless heaters.

This configuration will yeild your Ho 14.2 GPM. That is with a 60 degree rise in water temp. If you tell me the area these are installed, I can give you the exact temp rise. I did not see a detail for the inches of WC for the gassing. I'll assume they are installed to code. And I go out on a limb and assume the inspectors actually have a clue as to what they are doing....a rareity these days. Now, let's assume you already have all that, that I just described and it is still taking 2+ GPm to activate the heaters.......return them. I'm not joking....get rid of them. This will haunt you for years to come. You basically bought the Home Depot special in tankless (Paloma) which is a Rheem with a different sticker on the front.

The manual and spec sheet are far from technical. There is much to be desired, but they know the average plumber isn't going to understand much of that, so they give average / general info...that is not very conclusive. I could not find detailed info on multi unit performance, this is a bit troubling to me simply because I know exactly how the competition's units work. Those systems are just amazing in what they do....I found nothing on your units. Now, IF your setup is how Rheem wants it, and it does need that 2 GPM to fire, I know that these are not smart heaters...atleast the external controller is not very smart. Basic example: 3 units fire up to serve one fixture. What if the user doesn't want only hot on that fixture, how bout half hot half cold? Is Rheem seriously saying that you cannot get hot water?

How bout the same 3 units serving an apartment building...say 6 units. 2 in the morning someone wants to run their dishwasher...can they not?

Again, IF the units are installed as Rheem wants, disconnect one heater completely. Get rid of that stupid controller, and simply data connect one heater to the other. That will allow your HO to get activation with .6 GPM....while you figure out how to return these God awefull heaters. PM me if you need help and don't want the world to hear about it.

Good Luck

P.S. Oh I almost forgot

Check out: http://www.tankless-recall.com/

Rheem has some 42 thousand units that were recalled because they are killing people! Have a good night!
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Last edited by JamesNLA; 05-09-2008 at 12:04 AM.
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Old 05-09-2008, 12:03 AM   #15
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Re: Problems With Rheem Tankless Hot Water Heater Configuration?


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So does the Takagi, it has a built in flow sensor.
Any tankless heater that is digitally controlled has a flow sensor. I keep 3 of them stocked on my truck as it is the first thing to go when people have really hard water and do not do the service flush.
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Old 05-09-2008, 12:05 AM   #16
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Re: Problems With Rheem Tankless Hot Water Heater Configuration?


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Originally Posted by Double-A View Post
I would go back on Rheem on this one and demand they get their field rep to come take a look. If you have to exceed .66gpm on all units before even one will kick on, then I think they have a problem in their logic circuit.

I'm sorry I don't much about the Rheem units.
My thoughts exactly....on this size of a system, it's the least they could do. I personally wouldn't hold my breath in that they could actually fix anything.
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Old 05-09-2008, 12:09 AM   #17
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Re: Problems With Rheem Tankless Hot Water Heater Configuration?


Quote:
Originally Posted by Moscow View Post
We ran into a smilar problem here. we were told to install a recirc line to the last fixture on the branch worked great for 1 month then the contractor started having a problem with the tankless not meeting the demand. the final out come was a storage tank with a recirc line no problem for 6 months now however only time will tell.

not much help
good luck
This is a classic case that I see often of plumbers that are installing tankless heaters as if they were tanked heaters. Get rid of the storage tank...waste of energy. Is this in a hotel?
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Old 05-09-2008, 10:21 AM   #18
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Re: Problems With Rheem Tankless Hot Water Heater Configuration?


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Originally Posted by JamesNLA View Post
This is a classic case that I see often of plumbers that are installing tankless heaters as if they were tanked heaters. Get rid of the storage tank...waste of energy. Is this in a hotel?
how did you guess ? The great thing is it is not my problem.
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Old 05-09-2008, 04:18 PM   #19
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Re: Problems With Rheem Tankless Hot Water Heater Configuration?


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Old 05-12-2008, 09:30 PM   #20
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Re: Problems With Rheem Tankless Hot Water Heater Configuration?


Hey everyone - thanks for the replies.

I talked to a "tankless escalation rep" who was very helpful (on hold for 45 minutes) but it turns out my plumber installed the wrong cables from the heaters to the MIC-180 and the dip switches are incorrect. He says this is why it is not seeing the demand.

I have new cables on order. So we will see. BTW - these are installed in Texas.

@JamesNLA
OK, so if you don't like Rheem tankless and there are better units out there for the money, what are they? All the plumbers around here like the Rinnai.

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