# Tankless WH...48 psi pressure loss?



## gear junkie (Jun 20, 2008)

At a resturant and this has had the same reoccuring problem. Dishwasher kicks on, all hot water pressure in the place is lost. 48 psi coming in and 45 psi going out when a commercial faucet is on. Soon as the dishwasher kicks on, drops to zero psi...goes off, comes back up to 48 psi. It's a 3/4 pipe feeding it and it's never been cleaned in the 2 years it's been running.

I believe the 3/4 feed is enough...filled a 5 gal bucket up today in less then 20 seconds in the mop sink. I didn't have time to run a jumper hose from cold to hot and bypass the wh to ensure the dishwasher isn't just overloading everthing. That would be my next step along with a cleaning. Is there anything else I need to check...maybe some component that might cause the pressure loss?


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## Gettinit (May 9, 2012)

Does the place have a PRV? I would also check the backflow preventer.


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## OldSchool (Jan 30, 2010)

The tankless has a internal screen .. Did you check that???? ...should be on the cold side before it goes into the heat exchanger


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## gear junkie (Jun 20, 2008)

I haven't checked for either one because it's only the hot side affected. Do you think those components could affect the hot without affecting the cold?


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## gear junkie (Jun 20, 2008)

OldSchool said:


> The tankless has a internal screen .. Did you check that???? ...should be on the cold side before it goes into the heat exchanger


No I did not, didn't even know one was there. Thanks. 

Something to add, the hot side main valve was frozen...couldn't move it for nothing...if it was frozen halfway closed...this would have the same syptoms?


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## OldSchool (Jan 30, 2010)

gear junkie said:


> No I did not, didn't even know one was there. Thanks.
> 
> Something to add, the hot side main valve was frozen...couldn't move it for nothing...if it was frozen halfway closed...this would have the same syptoms?


Yes it would ... Somebody more than likely did that to throttle the flow to lower gpm out put because the tankless could not keep up ..


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## OldSchool (Jan 30, 2010)

Maybe install a prv on the dishwasher


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## Gettinit (May 9, 2012)

gear junkie said:


> I haven't checked for either one because it's only the hot side affected. Do you think those components could affect the hot without affecting the cold?


Not likely.


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## gear junkie (Jun 20, 2008)

OldSchool said:


> Maybe install a prv on the dishwasher


How would this help? 

Kicking myself for not running that jumper hose. I was right there but needed to get other stuff done.


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## justme (Jul 4, 2012)

I'd be surprised if the commercial dishwasher didn't already have a prv on it. All the big dishwashers we install here have them and they are set to 30 psi. Wouldn't hurt to run some cleaner through the tankless and check the strainer on the cold side.


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## justme (Jul 4, 2012)

Get that valve open or your working with half the volume.


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## gear junkie (Jun 20, 2008)

justme said:


> Get that valve open or your working with half the volume.


Not really sure if the valve is open. I tried to close it and the handle turned but the stem didn't.


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## JK949 (Mar 18, 2009)

How old is it? Does it have service ports? Has it ever been serviced? Is the gas probably sized?

If the second and third questions are answered with a no, draw up your paperwork to not be held responsible for any failures of the equipment if you decide to mess with it.

If you did not install it, they have NO warranty coverage from you. Don't be caught holding the bag for someone else's negligence.

Picture next time!


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## Fast fry (May 19, 2012)

Doesn't t matter how it works .just listen to old school


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## U666A (Dec 11, 2010)

fast fry said:


> doesn't t matter how it works .just listen to old school


this!^^^


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## gear junkie (Jun 20, 2008)

JK949 said:


> How old is it? *2 years* Does it have service ports? *Yes* Has it ever been serviced? *No* Is the gas probably sized? Never checked as this is a volume issue. Can impropper gas sizing affect the volume?
> 
> If the second and third questions are answered with a no, draw up your paperwork to not be held responsible for any failures of the equipment if you decide to mess with it.
> 
> ...


I keep forgetting the camera...


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## acid waste (Oct 1, 2012)

Most of These units have a pressure booster pump as well as a heating booster pump and when the pressure booster pump activates it will supply the upper and lower spray arms with the additional pressure needed to actuate or "propel" these arms. Some of these pumps can be up to 1 HP or larger depending on model so when it turns on it is pulling from the suction side of the pump like a $1000 dollar whore but alas to no avail... it is suffocating "sucking and sucking" faster than the supply can produce water which would explain your pressure loss to everything else, it is stealing it from the rest of the system. 

But that's just my "THEORY"

I would rather die on my feet than live on my knees Emiliano Zapata


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## acid waste (Oct 1, 2012)

O one more thing this unit as i mentioned also should have a heating booster that will give it a 40-70 degree heat rise in order to reach acceptable sanitation temperature of I believe 180 degrees. This means if your instantaneous WH set point is 115-120 degrees which will meet hand washing requirements as per health codes and with the heat booster rise of let's say 60 degrees, that will put you at 180 degrees +/- a couple.

I would rather die on my feet than live on my knees Emiliano Zapata


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## Jmcintyre99 (Jun 29, 2012)

Sorry I have not introduced myself yet but have had this problem before the tankless
Water heaters do not allow enough flow thought the heater to run a commercial dishwasher and another fixture at the same time tried booster pump and nothing worked had to add a small 10-20 gallon water heater to act as a storage tank in-order to make all work properly


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## Gettinit (May 9, 2012)

Jmcintyre99 said:


> Sorry I have not introduced myself yet but have had this problem before the tankless
> Water heaters do not allow enough flow thought the heater to run a commercial dishwasher and another fixture at the same time tried booster pump and nothing worked had to add a small 10-20 gallon water heater to act as a storage tank in-order to make all work properly


If sized properly they are good enough.


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## justme (Jul 4, 2012)

He has a point , it depends on the dishwasher and the heater sizing some of them run anywere from 5 to 10 gpm. Combine that with the heater hasn't been cleaned in 2 years and you have a problem. Hopefully Gear junkie can give us an update.


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## Jmcintyre99 (Jun 29, 2012)

I have to differ they say that the flow rate it one thing and it is drastically lower 
Have had this conversation with the rep for the heaters I installed in witch there were 3 which was almost double what they called for in proper sizing


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## Gettinit (May 9, 2012)

If piped and sized properly it is fine. The rep should know that but most reps are idiots.


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## Jmcintyre99 (Jun 29, 2012)

Well getinit 
I'm just speaking from my experience with them others may have had different outcomes


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