Little to no cold water in bathroom

[branimal]

My rental condo unit's master bathroom is getting very little cold water and then no cold water at all in the mornings (6-7am). So basically hot water coming out of the fixtures. This happens at all 4 fixtures. 2 sinks, a shower and a bathtub. It's been happening for a month.

The condo manager is hiring a plumber to inspect (shower body, faucets). He said he will bill me back if the issue is specific to my apartment.

I emailed the tenants to get more information.

There was water pressure work done recently for the unit's floor. There was a leak adjacent to the unit (not sure if that was supply pipe or DWV). There was also a new boiler installed 6 months ago.

I cannot envision 4 mixers malfunctioning at the same time. And only during specific time windows. FYI he is notorious for trying to bill owners for building issues. What could cause this?

 

[tarmy]

Ummm…their system is their problem. They should be paying for any fix.

If it is your unit, that you are renting, then call the owner to fix their stuff.

 

[kbuhagiar]

There was water pressure work done recently for the unit's floor.

Bingo!

Things like this don't just happen out of the blue, it requires human intervention.
Pretty sure this work is what is causing your problem. Somebody screwed up royally.

 

[branimal]

Started emailing some other owners on my unit's floor and the floor above.
1. One guy has the opposite problem. Not enough hot water.
2. Another guy has a loss of hot water pressure.

Building manager is going to be furious at me playing detective. I love it.

There's no way 4 of my mixers went out. NFW.

 

[DGersic]

I cannot envision 4 mixers malfunctioning at the same time. And only during specific time windows. FYI he is notorious for trying to bill owners for building issues. What could cause this?

Somewhere you’re getting crossover from hot to cold. A couple years ago, Dad went nuts fighting this in his own house, until eventually finding that Mom had decided that leaving the shower knobs adjusted to her preferred temperature was ok, and was only shutting off the hand-held shower wand thing. Once the knobs were turned off, the problem was resolved.

 

[branimal]

Somewhere you’re getting crossover from hot to cold. A couple years ago, Dad went nuts fighting this in his own house, until eventually finding that Mom had decided that leaving the shower knobs adjusted to her preferred temperature was ok, and was only shutting off the hand-held shower wand thing. Once the knobs were turned off, the problem was resolved.

Would that cause problems at other fixtures in the same bathroom? MY tenant's shower panel has a hot/cold temp dial. Set it and forget it. And the panel has a shower wand in addition to the overhead sprayer.

 

[DGersic]

Would that cause problems at other fixtures in the same bathroom?

His was causing problems in other bathrooms in the house.

 

[Tom Sestito]

In my old house, I have a similar problem - but it's because my cool water pipes are not insulated (and unreachable) and they pass right through the furnace room, which is hot. Also, the plumber laid the cold water pipes about an inch above the hot water pipes. So the ambient temperarture in my furnace room and the rest of the basement is warm enough to heat up my cool water - which means it take me upwards of 5 mins sometimes to get cold water. This is more of an issue in the winter, for me.

 

[Leaflessshadetree]

Strange that it happens at certain times and would be multiple fixtures. Occasionally plumbing work will dislodge scale or other debris from inside pipes. Usually will plug (maybe partially) aerators but could cause issues with mixing valves.
Happened with my shower. I was able to flush it by shutting off the hot water at the water heater and running the shower at full flow. Then shutting of the cold water at a valve and again running the shower at full flow.

 

[rlitman]

The usual culprit for these symptoms is a failed diaphragm in a shower body pressure compensating mixing valve. But there are certainly plenty of other ways you could end up with hot and cold mixing like this.

 

[finn]

My hot faucet in the Tucson house went from strong flow to a trickle.

Pulled the cartridge and found it plugged internally with tiny black bits of sand like material. In my case, it’s the faucet closest to the water heater. Works fine six months after cleaning.

In your case, I suspect contamination from the work done on the system jarred scale that’s plugging the cartridge.

Building owns this one.

 

[nadogail]

Good Luck in finding the cause of your problem.
If it happens to be Human Error, you can blame the previous tenant; no need to put yourself on report.

 

[four.cycle]

Do not do anything verbally.
Do everything in WRITING. Make copies.
Take photos.
Note date, time, name.

 

[branimal]

What I am trying to avoid here is the plumber showing up, turning some knobs, running the water and hitting me with a service call charge. It starts at like $600 IIRC. And coming up with some BS excuse as to why my fixture catridges are causing the problem.

There are three knobs on the panel.
Top = diverter: Options Shower head, body sprayer, or hand wand
Middle = volume control
Bottom = Thermostat. Set at preferred temperature.

Maybe its a problem similar to what @DGersic experienced??? I believe you shut down the volume control and the water stops flowing. I can't wrap head around how that would impact 2 sinks. And happening within specific time windows.

Shower Panel link.


**edit** - Maybe what you guys are saying about debris from construction messing up the shower cartridge is what's happening. How could I test that myself?

 

[firebirdparts]

I'm not sure you can. If water is always on to the "thermostat", then you have an obvious point where you could create this problem within your own apartment. It would be ideal to just shut off the shower, but I'm not sure you can.

I guess if you tell us the brand and model of that shower setup we could all go looking for the installation manual.

 

[DGersic]

What I am trying to avoid here is the plumber showing up, turning some knobs, running the water and hitting me with a service call charge. It starts at like $600 IIRC. And coming up with some BS excuse as to why my fixture catridges are causing the problem.

There are three knobs on the panel.
Top = diverter: Options Shower head, body sprayer, or hand wand
Middle = volume control
Bottom = Thermostat. Set at preferred temperature.

Maybe its a problem similar to what @DGersic experienced??? I believe you shut down the volume control and the water stops flowing. I can't wrap head around how that would impact 2 sinks. And happening within specific time windows.

Shower Panel link.


**edit** - Maybe what you guys are saying about debris from construction messing up the shower cartridge is what's happening. How could I test that myself?

Your shower panel should not be the cause, but it could be. Is that built in? Or added on later?

What Dad had was something like this:



The shower has two separate taps, for cold and hot. Dedicated shower, 1968 style. You get in, turn the knobs to get water flowing from the shower head, adjust temperature as needed. Was working fine.

Mom and Dad were getting old, and no longer felt safe standing in a shower. They added a shower chair, and a cheap wand. The kind that just replaces the shower head. That also worked fine. You got in, turned on the taps, and adjusted the knobs to desired temperature.

The problem started when Mom discovered that the wand had a shut off valve on it. Unbeknownst to Dad, she started leaving the taps on, so she wouldn’t have to adjust them to desired temperature. This wasn’t how the shower was designed to work, the in-wall plumbing allowed hot to cross over in to cold, and suddenly the sinks ran hot from both taps.

He spent quite a while trying to figure out where the crossover was happening. The biggest obstacle was that Mom had made a change that he wasn’t aware of, so didn’t think to look for.

Going back to turning the taps off resolved his problem.

Yours, I dunno. You have some kind of fancy diverter / mixer / valves panel thing there. It should (?) be designed to prevent crossover. It should be preventing crossover. But it seems possible that it has failed in some way.

Or, you’re in some kind of shared plumbing system here. It’s possible that one of your neighbors has something that is allowing crossover. Do all of your neighbors have this same shower panel? Were they all installed when the plumbing system was designed and built, or added on later as an upgrade?

Without understanding what you have and how it’s supposed to work, all I can do is speculate.

The only way I can see figuring this out requires checking everything connected to both hot and cold. Every sink, shower, has to be suspect. Depending on how the system is designed, it may be possible to isolate parts of it to narrow down where it could be.

 

[branimal]

Here's what I know: (I am rehashing a bit)
1. Boiler was replaced end of October 2025. We have oldish supply pipe. Copper sweat. ~50 years old.
2. We recently got some additional common charges for pressure work b/w 5th and 6th floor. My unit is on the 5th floor.
3. And charges for a leak b/w 5th and 4th floor. (Adjacent to my unit) - not sure if DWV or Copper pipe.
4. 6th floor unit above me has low hot water pressure after a recent shutdown (Early April)
5. Another 6th floor unit (adjacent to unit above me) has very little hot water during the same time my tenants have an issue.
6. There have been recent renovations in nearby apartments.
7. My risers come up and feed the vanity sinks, then supply the toilet. And then the shower. And then a separate bathtub. It is possible the shower catridge mixing components are damaged and allowing hot water to cross over to the cold line. This only happens in the morning. I think people are using more hot water (showers) in the morning than cold water (toilet). So the pressure on the hot side has to be so much higher than the cold side to over come the cold supply pressure so as to force hot water all the way back to the vanities. We're talking about a 10'x6' bathroom. So a lot of pipe distance and hence water volume. But I guess this is possible.
8. If the hot water pressure is that high, why is one unit on the 6th floor not getting enough hot pressure. And another unit is getting too little hot water. He ends up taking cold showers.
9. My tenants turn off the water and go to the 4th floor bathroom to get ready. (It's a duplex). No problem in that bathroom.
10. Lets go back to the new boiler. ITs a boiler not a hot water tank supplying hot water. So there is a master mixing valve. It takes 180F water and mixes it with cold to achieve ~120F. There could be some failure at the mixing valve.
11. There is also a recirculation pump. Keeps hot water available so you don't have to wait for it on the higher floors. 6 story building.

My guess is when balancing the pressure on the recirc pump, something went wrong. Too much pressure on the 5th floor and too little pressure on the 6th floor.

 

[The Cobbler]

you definitely have a flow issue . I won't try to diagnose it over the internet
to strengthen your case get a thermometer under the tap when it's doing the cold thing, take a video of opening the valve and measuring the temperature and send it off to them . that would be very tough to dispute ( even in court) if they do bill you. also get date/ time stamps from your cell phone

 

[branimal]

you definitely have a flow issue . I won't try to diagnose it over the internet
to strengthen your case get a thermometer under the tap when it's doing the cold thing, take a video of opening the valve and measuring the temperature and send it off to them . that would be very tough to dispute ( even in court) if they do bill you. also get date/ time stamps from your cell phone

Good idea on the thermometer. I'll amazon a thermometer over to my tenants.

So I thot about this some more.... if the water at the shower is too hot b/c of a failed catridge and backfills the cold line back to the faucets, and the faucets are turned cold and hot water comes out. Then the temp regulator catridges at the faucets (two if them) have also failed.

The probabilty of that happening is slim. But then magically this is not the case later in the day..

 

[75gmck25]

I'm sure there are shutoffs under the sinks, but are there also shutoff valves for each line to the shower controls?

If you could shut off the lines to each fixture but one, and then try the same test where you got hot from the cold line, maybe you could determine where the hot water is crossing over to cold.

Another simple experiment is to shut off the hot water at the water heater, and run the same test with the cold line. If you then get real cold water, there is definitely a cross-connect somewhere.

I have also had problems with grit getting into a shower control (internal holes in the control are very small), and then throwing off the temperature for that shower. I think it may be the pressure balancing valve gets out of whack because one side is nearly plugged and it is still trying to balance the pressure.

 

[jhelrey]

Somewhere you’re getting crossover from hot to cold. A couple years ago, Dad went nuts fighting this in his own house, until eventually finding that Mom had decided that leaving the shower knobs adjusted to her preferred temperature was ok, and was only shutting off the hand-held shower wand thing. Once the knobs were turned off, the problem was resolved.

I work in commercial real estate. The cleaners do this, but with the soap dispensers for mops. They turn the valve off at the hose. I didn't realize how often they did this until I'd shower after the gym and have hot water and hotter water. I solved the issue by shutting off the hot water to their janitor sink.

The issue is hot water gets to places where it shouldn't be. Urinals, toilets, etc. Wax rings don't like hot and the women don't like their *** feeling like it was in a sauna.

It's a HUGE problem and cause issues in an entire building.

 

[branimal]

I think I figured out what's going on..... lmk if im off base. (I own Apt 501)

• Apt 602 – when he has water temperature issues, it’s because there isn’t enough hot water to mix with the cold. This happens in the mornings. This is the inverse of the issue Apt 501 is experiencing. (Too much hot water in the mornings). Perhaps hot water is getting diverted before it reaches 602's pipes.
• Apt 601 – has been experiencing significantly less hot water pressure in the kitchen since a recent water shutoff
• XYZ Plumbing has recently done work to address water pressure issues on the 6th & 5th floors.
• XYZ Plumbing has recently done work to repair a pipe leak from 502 to 402.
• New Boiler installed (~October 2025). New boilers exert higher effective pressure on the pipes than our decommissioned boiler. I would guess the majority of our riser and branch lines are from the mid-1980s.
• Apt 501 – Very limited cold water in the mornings (~615a – 715a). After a few minutes the water is unusable at the shower and two sinks. This is the exact time slot that 602 is experiencing “not enough hot water”. Because 501 operates perfectly outside of this window, the internal hardware (shower cartridges/faucets) is clearly functional.
• Apt 501’s shower, vanity sink 1 and vanity sink 2 are getting hot water when turned to the cold position during morning rush hours. What are the chances that all three cartridges are damaged at the same time? And then start working outside of the stated early morning hours.
• 
  
• It could be a pressure balancing issue at peak load time. There is high hot and cold water demand in the morning. (Showers/Toilets). Hot water is pressurized by a recirculating pump/ variable speed pump (new boiler). Cold water relies on street pressure. So hot water pressure becomes higher than cold water pressure and pushes into the cold lines. When water demand drops (after peak morning hours), the hot water recirculation pump reduces pressure. Hot water pressure and cold water pressure get closer to equilibrium and there is no crossover from hot to cold. This would explain the phenomena we are witnessing in the morning hours.

I don't know if we have check valves under our shut off valves. I don't recall seeing one when my bathroom/kitchen was renovated.

 

[The Cobbler]

Many years ago I was involved in a multi small office building that was heated with Hot Water .
there was an issue with the heat in 2 offices, basically one would get no heat when the other was calling for heating .
It probably was never an issue or even noticed until we divided 1 large office into 2 smaller offices . The division was where the 2 thermostats separated the heating circuits so it shouldn't have been an issue as each smaller room was on a separate circuit so to speak .
After crawling around in a crawl space under the building, I forget the exact reason why it was acting like that because it's many years ago... but it was something like when the first office stat was calling for heat the flow to the second office was bypassed so the line of least resistance was the return to the boiler, not thru the heating rads to the second office .
that was a fun repair , bent over on my knees , working with old threaded black pipe ... but I was in my 30's and a lot more flexible than I am now .

 

[dscheidt]

I work in commercial real estate. The cleaners do this, but with the soap dispensers for mops. They turn the valve off at the hose. I didn't realize how often they did this until I'd shower after the gym and have hot water and hotter water. I solved the issue by shutting off the hot water to their janitor sink.

Good mop faucets have check valves to prevent that. So do restaurant prerinse faucets, which can cause the same problem, because no turns off the water at the knobs, they rely on the sprayer valve.

 

[Milton Shaw]

My hot faucet in the Tucson house went from strong flow to a trickle.

Pulled the cartridge and found it plugged internally with tiny black bits of sand like material. In my case, it’s the faucet closest to the water heater. Works fine six months after cleaning.

In your case, I suspect contamination from the work done on the system jarred scale that’s plugging the cartridge.

Building owns this one.

Check your washing machine and dishwasher they may be clogged too, could be an anode in the water heater. I have seen them clogged and owner never recognized them until Dishwasher would not clean dishes as it was not getting any water.

 

[finn]

Check your washing machine and dishwasher they may be clogged too, could be an anode in the water heater. I have seen them clogged and owner never recognized them until Dishwasher would not clean dishes as it was not getting any water.

Flushed the water heater and got calcium deposits to come out.

Water heater really needs replacing, given the poor water quality in the Southwest. Don have that issue at the UP house where water is natur soft.