Talkless Water Heater & Pressure Drop

14 years ago

Hi,

We had a Noritz tankless water heater installed in our home 4-5 years ago. Ever since, the hot water has been pouring out at less pressure than the cold water. What is worse, is the hot water will decrease even more when two faucets are using it at the same time.

I am thinking that either the company that sold us the unit undersized it, or we need some kind of a device attached to it to regulate the pressure. We are in the middle of a remodel, and I would like to get this problem that has been overlooked for far too long fixed.

Thanks!

Sort by:Oldest

Comments (5)

baymee
14 years ago
Did anybody reduce the pipe diameter anywhere in the line? Also, do you have hard water? In this area, the limestone hard water can block up a coil in 3 months.
jake2007
14 years ago
Under normal desperation there is some pressure drop with tankless units, but it shouldn't be that noticeable with just a faucet.

Tankless units do restrict the output to maintain water temp, however. So, once they start exceeding their capacity they start restricting output instead of allowing the temp to drop.

Tell us what we need to know in order to size a unit:
-How cold is the incoming water at the coldest time of year.
-How many hot water faucets - and what type - do you normally run at the same time.
-The model (or BTU/H rating) of your current heater
Related Discussions
intermittent low pressure from new hot water heater
Q
Comments (3)
If I were going to guess, it would be that you got the two sides reversed. That is, you connected the cold to the outlet and the hot to the inlet. Most all the new WHs I see have a restriction valve in the inlet and outlet to make sure that hot water does not flow out the cold side.
...See More
Water heater pressure relief valve leaking. Advice needed
Q
Comments (8)
The valve you are talking about is a pressure relief valve (PRV). It is a safety device to prevent WH explosions. Either the valve is bad and needs to be replaced with EXACTLY the same spec valve despite what a vest wearing know it all at a box store says... "this one fits everything". Or you have a closed plumbing system and you have a thermal expansion problem that needs to be corrected NOW. If you have a closed plumbing system, and that has been code since the 90's, there should be a small thermal expansion tank installed proximate to the WH. These tanks have a bladder that may have failed and the tank must be replaced. OR... you have a closed plumbing system and there is no thermal expansion device installed, which is not uncommon, and there needs to be one installed. In this case the PRV is acting as a thermal expansion device and it is NOT intended to. Here's some light reading on thermal expansion... http://www.watts.com/pages/learnabout/thermalExpansion.asp If this seems beyond your skill level call a plumber... and do it SOON.
...See More
water pressure for refrigerator water dispenser
Q
Comments (34)
Now that you know you have a PRV we KNOW you have a closed plumbing system and the 100psi spikes are the result of thermal expansion. You can refer to the link 14 posts above for a detailed explanation of thermal expansion. The PRV creates a closed plumbing system. Since your internal pressure is 60 psi we can assume that portion of the PRV is working. We can prove that if we know the street side pressure. The N35B does have a built-in bypass feature that limits the internal pressure to 10psi above the supply pressure. I don't trust the built-in bypass because the intent of a closed plumbing system is to prevent back-flow into the main system from homes. Click here for N35B details and read the TROUBLESHOOTING section CAREFULLY. You may be experiencing the dribble now just because the new fridge has a valve that is sensitive to excess pressure. The bypass on the PRV might have just failed and is now causing you a thermal expansion problem. That is why the preferred thermal expansion control device is a thermal expansion tank. Here's what I would do... 1. Measure supply (street side of the PRV) pressure for reference and to know how much the PRV is reducing the pressure for future troubleshooting. 2. If the PRV is not reducing pressure then replace it. 3. Install a thermal expansion tank at the cold inlet for the WH and sized from the link 14 posts above including a 1/4 turn ball valve so the tank is easily serviced in the future. 4. When that is done, if the fridge leak persists then back to GE, BUT, without a receipt from a plumber you may be banging your head against a wall with them unless you get a GE tech that has field experience and is knowledgeable.
...See More
well water/on demand water heater
Q
Comments (12)
update - did all the checks from Bosch instructions and checked filters on all fixtures in the house. The two fixtures that had most dirty filter were kitchen sink and guest bath sink. The inlet water filter in the heater was a MESS - lots of clay dirt, tiny pieces of grass, and its physical condition is not good so it has to be replaced. We took it out and continue to use the heater as normal until we get replacement. It costs $7, and $7 shipping, so I am going to buy two - for the same cost of shipment - to make it worth the cost. Now that we have big filter in main line , this little one should not have too much work to do. I also changed a rubber washer in our showerhead to open water flow. I know these reducers are designed for city people to reduce their water bill, and we had it in the city, but now we dont need it. All this really opened up water flow and reduced problem but not completely. Right now temp setting is at 104, but the outlet hot water pipe temp reads at 115F. We should still do the multimeter check of the water temp sensors. But I was able to enjoy shower for the first time in longest time. Definately a noticeable improvement so thank you all! also, our PRV does not have a tap to check the pressure, so we will install a gauge in the line, and while we are at it - we will re-arrange the order of filter and PRV.
...See More
iceqween13
14 years ago
We bought a Noritz N-631 a year ago and immediately could tell it was not enough flow. We added a second Noritz but the company we purchased & installed them from installed a N-751 - however Noritz recommended they be the same model numbers.

So, after a year we now have two tandem N-0842 condensing models which made a huge difference with flow. And we can turn on more than one tap. Our water is C O L D.

This was costly endeavor and I personally would never recommend tankless hot water tanks. We could have bought numerous electric hot water tanks over the years for what we paid.

Also, we turn on the tap and let it run until the hot comes through - then turn on the washer or dishwasher - then turn it off. Takes too long to get the hot through otherwise.

We found Noritz VERY good to deal with and provided good information.

Good luck with your tank.
arazavi
Original Author
14 years ago
@baymee, we do have hard water. I am in the process of sizing and buying a water softener to fix this problem. I believe the city water report stated 18gpg hardness averaged out.

@jake2007
How cold? I never ran a temperature test, but I would have to say ice cold, which is rather cold for SoCal.

How many hot water faucets at the same time? 2-3 shower heads, or 2 showers and a washing machine. The heads are some inexpensive ones we found at home depot, that don't have a large output capacity that more expensive ones do.

Model number - N-048M

Thanks for the replies thus far.
jake2007
14 years ago
arazavi,

In order to size a tankless heater you have to know (or approximate) the cold water inlet temperature... descriptions like "ice cold" and "very cold" aren't very useful to plug into a formula. Where I live I've measured it down to 33 degrees when it was -15 outside.

A standard shower head is limited to 2.5 gal a minute. A top loading washing machine is 4+ gpm. You are using between 5 and 9 gpm.

I was unable to find the "N-48M" heater that you described. Are you sure you didn't switch a couple of numbers?

At any rate, a 200k btu/h heater will heat 8.5 gpm only 35 degrees. So, if you have 9 gpm you will be under that.

At 5.5 gpm (two showers) it would heat 45 degree water to 105 degrees - which is the design temp for a shower.

In other words, depending on your real cold water temps and the actual unit that you have, you may be undersized and causing the drop that you are speaking of. Remember, these units will throttle the hot water output if you exceed their capacity.

Get back with better information and we may be able to figure this out.

Talkless Water Heater & Pressure Drop

Comments (5)

baymee

jake2007

Related Discussions

iceqween13

arazavi
Original Author

jake2007

COMPANY

BUSINESS SERVICES

GET HELP

CONNECT WITH US

Talkless Water Heater & Pressure Drop

Comments (5)

baymee

jake2007

Related Discussions

iceqween13

arazaviOriginal Author

jake2007

COMPANY

BUSINESS SERVICES

GET HELP

CONNECT WITH US

arazavi
Original Author