Low Hot Water Pressure in Upstairs Shower

[Bosley]

I recently moved into a house and am trying to diagnose a hot water pressure issue in the upstairs master shower. The water heater is in the basement. I have two showers upstairs with the same shower head, one with two handles (hot and cold) and the other with a single lever. I put the shower head with good pressure on the low pressure shower, verified that pressure was still low so it is not the shower head.

To verify my suspicions, I timed how long each shower took to fill a 1.5 QT container, one time using just hot and one time just cold (or pushed all the way to the hot or cold side for the single lever).

Low pressure shower: 20 seconds (just hot), 8 seconds (just cold)
Good pressure shower: 7 seconds (lever all the way to hot side), 8 seconds (lever all the way to cold side).

I'm handy so I'd like to at least identify the problem before I call in a professional, but I'm least familiar with plumbing and would appreciate any guidance. Thanks!

 

[Dj2]

From your description, the slow hot is with the two handle faucet. Correct?
If yes, I suspect your hot side valve is faulty.
Remove the handle on the hot side, then remove the flange and take a good pic of the valve in the wall.

 

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[Bosley]

Yes, the two handle hot is the problematic one.

So it's got a rough in valve and then what appears to be a screwless handle. I poked around the faux cap but it doesn't appear to be budging. Any suggestions on how to get the handle off? And do I need to remove the rough in valve as well to access the valve? Thanks for the help!

 

[Jadnashua]

If the low-pressure unit's valve has in-line shutoffs or particle filters, the shutoff may not be fully opened, or the filter screen has debris on it. You'd need to pull the trim cover to see if the valve has in-line shutoffs. It may not be obvious whether there are any filter screens, but that's usually obvious if you have the installation/parts list manuals.

Plumbers on the site have noted all sorts of things IN the pipes that could limit flow.

People get volume and pressure mixed up or do not understand. What you're noticing when measuring flow is not a pressure issue, it's a volume issue since other things in the house seem fine. So, anything that could restrict the volume would need to be checked to isolate the problem.

It's also possible that inside the cartridge there's an obstruction...so, just changing it might solve your issue.

Sometimes, people have cleared debris from first turning the main water off, removing the cartridge, then have someone carefully turn the main line back on. That would also allow you to compare the volume of both the hot and cold inlets to the valve. Water WILL go everywhere, so have communications to the person turning the main valve on/off and start slowly.

Because of the (usually) longer path from the WH to the shower, it's not uncommon for th eadded friction to drop the pressure on the hot line sligthly, but it's often not much. If no water was running, and you measured the pressure, the pressure would likely be identical between the hot and cold. So, the DYNAMIC versus STATIC pressures are often different in a fluid distribution system because of pipe diameter, distance, and fittings (primarily, changes of direction). No flow, or static conditions, things should be the same. Dynamic, things flowing, is where things change.

 

[Jadnashua]

Appears you were typing as I was, and your post got there first!

On a two-handle valve, there is no rough-in valve, the valves you see are the operational part, at least for most.

You could remove the stem and try to flush the line. While you have it out, you could check to see if it has a washer that seals, or it's a cartridge. Not sure how that comes apart, but you may find that the two handles and whatever is in between comes off the wall as an assembly if you loosen the nut at the base. I'm guessing, but think it may be a washerless cartridge.

 

[Bosley]

I appreciate all clarifications on terminology and parts!

You were right that it came off as a unit. There was a rubber washer as well that wasn't pictured. I didn't see any blockage at first glance.

 

[Bosley]

Here's video of turning the main shut off on. The cold water stream had significantly more volume than the hot water stream.

 

[Bosley]

So based on what I'm seeing the only idea I have before calling someone in is a hot water backflush. Any other ideas? I appreciate the help!

 

[Bosley]

Back flushing the hot water line didn't have anything come out but water, and water volume/pressure afterwards was still no where close to the cold water pressure. Any other ideas? I appreciate the help!

 

[Jadnashua]

Remind me, is this at only one location? Anything else using hot water at the time?

If it's at all hot water locations (may be harder to determine, depending on the type of device), then that would lead back to the WH. Sometimes, they use heat traps on the in/out. If either one of those has failed, it could restrict the flow. Even if no heat traps, if they used flexible lines, as the internal waterproof layer degrades, it could plug up the outlets. Worst case, it's possible that mineral deposits might have formed.

Make sure that the shutoff to the WH is fully opened.

 

[Bosley]

We have two full baths upstairs. One has great got water pressure in shower and sinks. The hot water in the trouble bathroom shower flows at half the rate of the good one. It's likely that the hot water sink lines in the trouble bathroom are also affected, but I've only specifically tested the shower. No other hot water was being consumed at the time of any of the tests. WH valve was open all the way.

If I had to guess the flow of the pipes, I think the water flows up from the WH and has a short horizontal travel to the good bathroom. The trouble bathroom has another 20 feet of horizontal travel if the pipes run the way I think they do. Could that make a difference?

 

[DIYorBust]

What kind of pipes do you have? I had this problem in my super old house and found a section that needed replacing.

 

[Jadnashua]

20' of most piping might lose a couple of pounds of dynamic (while water is flowing) pressure, but not a significant amount of volume. That assumes that the pipe is in good shape.

If there are ANY bits of galvanized piping used in the shower that isn't working well, that could easily be your restriction. Hot water tends to corrode the galvanized piping much faster than on the cold side. Most galvanized stuff is plated prior to cutting the threads, which leaves those areas entirely unprotected. Plus, over the years, imperfections in the interior will allow rust to begin. It can easily restrict the piping significantly.

One thing you could look at is the elbow used to hold the shower arm...remove the shower arm, and see if the fitting is brass or bronze, versus maybe even plain black iron or galvanized. You may be able to use a flashlight and take a close look. If you can't see it well, a magnet will let you know if it's ferrous or not.

 

[Bosley]

House built in 96, I'm not sure how to find out what kind of pipe is used throughout. Removing the handle fixture, the pipe goes a few inches and then hits an elbow. To me the pipe looks copper, but picture attached as well.

 

[Jadnashua]

The color of wet, rust, looks sort of like copper. If you have something with a small magnet, that would be the definitive test unless you can take something and lightly scratch it to see what's underneath. Color pictures can be deceiving depending on the lighting and the monitor they're displayed on. If you look at the end of the shower arm you removed, does that look like it's rust, or is it clean other than the pipe dope or tape?

 

[Bosley]

Didn't see any rust or other residues in the fixture I removed. But magnet does not stick to inside of pipe.

 

[Jadnashua]

Well, not ferrous, then it's not steel, so that part rusting isn't the issue. I'm out of ideas. I think you tried it without the showerhead installed, so that and that fitting in the wall being open aren't the issue.

Is the wall behind this something you could open up to gain access and look?

 

[Bosley]

We'd be cutting drywall to access it, and we just can't bring ourselves to do it yet, too much other stuff going on at the moment. I appreciate the help though!

 

[DIYorBust]

In this situation, rather than trying to repair the piping behind the wall, you could look at trying to bypass that entire segment of pipe, perhaps by fishing pex up from below and cutting only a small section of the drywall to tie in. To avoid a dead leg, and get a bonus, perhaps you could tie the line into a circulation pump. The limited capacity of the clogged line would likely be enough for circulation. Just a thought.