Low Pressure at Faucets After New Water Heater

Hi all,

I'm now to these forums so thanks for taking the time to read this. I'm totally stumped (and so was the plumber I called out) so I'm hoping you guys might be able to point me in another direction. Sorry for the long post, but This has been a multi-level issue. Here's what I've been dealing with:

I recently installed a brand new water heater (AO Smith) in my house. After I installed it, I found that I was barely able to get any hot water to any of the faucets in my house. Two-handle faucets where I could turn just the hot water on would run hot, but very low pressure. Anything with a mixing valve wouldn't get more than luke warm.

I first discovered that my PRV had gone bad. Pressure at the front hose bib (closest to the meter) was 100psi. I got a rebuild kit and installed that and brought the pressure down to 70psi.

I next discovered that the mixing valve in the master bath (closest taps to PRV) had a failed cartridge which was causing crossover. Shutting off the service stops to that valve solved the issue of not getting hot water to the rest of the house.

But now the water pressure in the entire house is extremely low - especially on the hot side. All of my hose bibs and the drain bib on the WH all show 70 PSI but the flow is super low inside. If I turn on two hot taps at once, both will just dribble.

I verified by watching the micrometer that there's no leak. I've confirmed that the WH lines are connected correctly and the water is heating up. I shut off the source of the crossover (for now).

What's my next move?

You say, "But now the water pressure in the entire house is extremely low - especially on the hot side. All of my hose bibs and the drain bib on the WH all show 70 PSI but the flow is super low inside. If I turn on two hot taps at once, both will just dribble"
Are you saying that the cold, although not as low as the hot, is extremely low, also?

When you check pressure at the drain bibs, I assume you are NOT running any water. In other words, just checking STATIC pressure?

A proper pressure check, to help find the possible location of pressure loss, must include a flowing condition.

Ideally, having a hose bib, to attach a pressure gauge, in many locations would help locate the area of pressure loss. But I know you don't have many locations where you can screw on a pressure gauge. Other places may include, Washing Machine hook ups and water heater drain.

For example: If you were to check the pressure at the water heater tank drain with water flowing at some HW fixture, you may find the pressure is high at that point, since the pressure loss is not UPSTREAM from there.

Whereas, if you where to test the pressure at the HW side of the washing machine you may find substantial pressure loss. If so, the loss could be taking place between the water heater and the HW line feeding the washing machine.
Then try it on the CW side of the washing machine. You may not find any substantial pressure loss.

In other words, we're trying to find the device or piping that causes excessive pressure loss when flowing water through it.

How about a picture of the top of the water heater showing Hot and Cold water piping connections.
Did you do any soldering close to the tank connections?

Thanks for the reply!

The cold pressure also seems low, but it's not as dramatic as the hot.

You are correct about the static pressure. The WH drain reads 70 psi with no water flowing anywhere. It drops to 60 psi when I run hot water from a tap. I'll need to check if that same pressure drop is showing when I have cold water flowing and I can check the all of the hose bibs for that pressure loss as well. I haven't checked the pressure at the washing machine bibs, but I'll do that as well when I get home later.

Unfortunately, I don't happen to have any pics of the WH connections with me, but I'm certain they are correct and the plumber I had out confirmed that as well. There was no soldering done to make any of the connections and I replaced the supply lines with brand new braided stainless hoses. The previous lines were copper flex, but would that make any difference? Perhaps the new hoses have a smaller ID reducing flow?

ErikPiazza said:

Thanks for the reply!

The cold pressure also seems low, but it's not as dramatic as the hot.

You are correct about the static pressure. The WH drain reads 70 psi with no water flowing anywhere. It drops to 60 psi when I run hot water from a tap. I'll need to check if that same pressure drop is showing when I have cold water flowing and I can check the all of the hose bibs for that pressure loss as well. I haven't checked the pressure at the washing machine bibs, but I'll do that as well when I get home later.

Unfortunately, I don't happen to have any pics of the WH connections with me, but I'm certain they are correct and the plumber I had out confirmed that as well. There was no soldering done to make any of the connections and I replaced the supply lines with brand new braided stainless hoses. The previous lines were copper flex, but would that make any difference? Perhaps the new hoses have a smaller ID reducing flow?

Click to expand...

Sounds like the problem is much more than new hoses having a smaller ID reducing flow.

Just to make sure you have a handle on where/how pressure loss is occurring, in the case of the 10 psi drop when flowing anywhere in the house, it's losing that 10 psi pressure only in that piping between the main supply and the tee where the hose bib gets fed from. And that's a function of GPM, size of piping and length of piping. All values can calculated when GPM, pipe size and length of pipe are known.
Not to confuse you but if you get it fine. If you don't, don't worry about it.

High pressure will not translate into flow if there is a blockage, so I am guessing somewhere at the WH is where the problem lies. Flow is dependent on friction or occlusion.
First off, pull the nipples and remove any "heat trap" that may be there.
Sometimes a floating ball in the dielectric nipples, sometimes a rubber flap assembly just at the tank threads.
If none of those items are present, then flow test out of the water heater into a bucket or hose to outside.

I totally appreciate the info even if I have no idea how to actually calculate for all the GPM, etc! I didn't think the new hoses could be the issue either, but just trying to provide as much info as possible since this is such a head-scratcher.

breplum said:

High pressure will not translate into flow if there is a blockage, so I am guessing somewhere at the WH is where the problem lies. Flow is dependent on friction or occlusion.
First off, pull the nipples and remove any "heat trap" that may be there.
Sometimes a floating ball in the dielectric nipples, sometimes a rubber flap assembly just at the tank threads.
If none of those items are present, then flow test out of the water heater into a bucket or hose to outside.

Click to expand...

Yes , I was thinking WH restrictions, but some of the other symptoms (cold water pressure reduction) make me wonder.

When you say, "flow test out of the water heater into a bucket or hose to outside" are you saying from the drain connection? Which would be checking the cold water feed to the WH. If he can incorporate a pressure gauge at that point, it would be a meaningful test of flow vs pressure TO the WH.

OP...you say you have a PRV on your main service line.
Do you have anything else, like a filter and/or softener system?
I assume you have an expansion tank for the cold water feed to your water heater? Was the air pressure reset to match your incoming water supply pressure? And was it done correctly?

Yes, I do have a water softener. If there was a blockage there then I assume I woudn't be getting 70 psi at the WH drain, but I'll bypass the softener just to make sure.

ErikPiazza said:

Yes, I do have a water softener. If there was a blockage there then I assume I wouldn't be getting 70 psi at the WH drain, but I'll bypass the softener just to make sure.

Click to expand...

Wrong!
Partial blockage doesn't stop static pressure. It would have to be completely/tightly isolated, like with a valve.
A pinhole will allow a 70 psi static pressure reading.

DO YOU HAVE AN Expansion tank for the cold water feed to your water heater?
Was the air pressure reset to match your incoming water supply pressure?

Ok, good to know about the softener! I'll bypass it and see what happens. There is no expansion tank on the WH.

I really appreciate all the help!

Diehard said:

Wrong!
Partial blockage doesn't stop static pressure. It would have to be completely/tightly isolated, like with a valve.
A pinhole will allow a 70 psi static pressure reading.

Click to expand...

But a pressure reading at the WH when flowing, with and without the water softener wouldn't hurt.

The softener will have an inlet screen, which is very easily clogged up with minerals stirred up by changing out the water heater.

You can find the manual for your softener online, along with the procedure to clean the inlet screen.

Do you also have a whole house water filter?

My softener is provided by a local service and they come out to replace the tank/salt every other week. It's upstream from the WH so I don't understand how sediment from the WH could ever get there to clog it up, but I'll take a look and see.

Did you install the water heater yourself?

If you had a plumber install it, have them come back and fix the issue caused by the new install.

And make sure all valves are open, sometimes things get turned off or partially off, then forgotten about.

And don’t confuse flow rate with pressure.

Your problem seems to be low flow rate.

I installed the WH myself. I've done several of them before, including the one I just replaced, and have never had any problems. Regardless of that and recognizing that things change and I'm not a professional, I still called a local water heater guy who was kind enough to ask me a bunch of questions and review some photos and confirm that everything looked right. And then I also had a plumber come out who verified that the WH was installed correctly and was only able to conclude that there was crossover somewhere in the system, but couldn't find it in the 2.5 hours he was there.

Yes, I understand and agree that it seems like my issue is more likely flow than pressure.

There are so many factors so just to recap...

1) New water heater installed, but then very little hot water getting to any faucets
2) Discover bad PRV - house getting 100 psi
3) Crossover found in master bathroom shower mixer valve
4) Crossover eliminated by closing service stops to bad mixer valve (will replace)
5) PRV rebuilt and set to 70 psi (only set this high because pressure at faucets is so low)
6) Numbers 4 and 5 result in hot water to all faucets, but flow is very low.

Whoa...
You had a PRV(Pressure Reducing Valve) that had gone bad. Pressure at the front hose bib (closest to the meter) was 100psi. You got a rebuild kit and installed that and brought the pressure down to 70psi.

I assume you had a Water Heater before you installed this one. And you say you do not have, nor previously had, an expansion tank anywhere between your PRV and your Water heaters cold water inlet???

Did you have elevated hot water pressures occasionally cause your water heaters T&P(Temperature and Pressure) Relief Valve to spit/dump water??

What size was your previous and present water heaters? What temp do you keep it at?

If you have a PRV(or anything) which prevents the hot water from expanding back into the cold water source, you are subject to blowing your P&T Relief Valve.
You should have an Expansion Tank designed for potable water that is pre-charged with air pressure equaling the water source pressure. This provides air space within the tank for the purpose of accommodating the hot water expansion when it heats up.

Never had an explosion! lol. Also have never had the T&P valve on the old WH spit anything that I know of. We've usually kept the WH set pretty high (not all the way to "very hot" but getting there). I know about expansion tanks, but I've never had one.

Just saw your last post.
FYI...A flow issue is a pressure issue. They go hand-in-hand. The higher the pressure the higher the flow and vice versa.