Googling seems to show this problem often caused by a bad faucet or shower valve. (Moens seem be mentioned often) Some valves have a ‘pressure balancing spool’ which prevents the water from becoming too hot when someone flushes the toilet, but these can fail, blocking either the hot or cold water.
It also can happen that water from the water heater can back up into the supply line, heating the cold water.
From waterheaterrescue
I don’t have day-to-day data on this, actually, but I do recall once about 6-12 months ago … I was sick and throwing up in the toilet very late, about 3:00am. I flushed the toilet several times during this.
Although I did not put my hand or face into the water, I was gripping the sides of the bowl, and noticed that it was very hot after the first few flushes, but not right away.
I’d have to guess we don’t notice this under normal use because the water in the bowl, and the water in the tank, are both cold, and on a low-flow toilet, it’s going to be at least 2, maybe 4 or a lot more flushes before you cycle in hot water, depending on how far from the toilet the hot water source is.
That one morning, I had flushed it several times before noticing the temperature, and haven’t noticed it since. I don’t know much about plumbing inside the walls n stuff, so I don’t know how closely related the toilet is to the shower and the sink, but it’s between the two.
We got one of those setups where the toilet and shower are in one room, and the sink is in the next room, which is really the hallway between the bedroom and the living room. It’s kinda cool if you haven’t seen them before, but I mention it because it may mean we have different wall plumbing than other people, which may have a bearing on this conversation.
There was one other time where, early in the morning, the toilet was stuck up in one of those situations where it drains real slow and takes several flushes to fix. (If you don’t have the primitive model of low-gpf toilets, this may not have happened to you…)
After 8 or 10 flushes, I proceeded to use the toilet, and noticed my bottom-side was getting steamed! Obviously it wasn’t boiling, but it was very hot and humid inside the bowl. So that’s two instances of hot water occurring inside the bowl – once it hot enough to be felt through the porcelain sides, once hot enough to slowly cook my nuggets (or at least feel like it, that’s an odd sensation when you’re outside of a steam bath…)
I had Googled this myself several times over the past year, and every time I found something new I would call the apartment manager and suggest it to her. She would always dismiss what I read on the Internet as a crackpot idea.
The link you gave is suggested by someone in a house with an electric water heater, where the water in the cold faucet goes from cold to hot to cold.
In our situation, it starts out hot immediately and stays hot consistently for 20-30 minutes. The water heater is a gas one, and it is gigantic and serves several apartments and probably the washer (the laundry room is right next to it). We’ve never, ever run out of hot water, it must be super industrial strength or something.
The solution might be to videotape the problem, ‘cold’ water running over a thermometer, and send a copy to the landlord. Let him/her know that if he doesn’t take this problem seriously, and do whatever it takes to track down the problem, you will be reporting what I am sure is a code violation. This is a safety issue.
My girlfriend kind of suggested that it might come to that.
I got a good camera already, can you recommend a good thermometer to measure the temperature? My normal one would drown 
In our place in Dubai the water heater is in the air conditioned house. In the winter we turn on the water heater and get cold water from outside and hot water from the heater - all is normal. In summer, we never turn on the water heater and it provides cold water. The water from the “cold” tap comes from outside where it is 120F and generally the water is too hot to touch. It is tricky getting it right during the short spring and fall seasons.
Are you in a HOT climate?
Compared to Dubai, nothing is hot. That being said, I’m in Southern California (a valley near the LA basin) and it does get hot here in the summer. It’s 94 Fahrenheit right now, we spent a couple months over 100 and sometimes over 110, but the water will be that hot even when it’s only 70 degrees outside.
This whole “solar heating of the pipes in the attic” theory has got to be bunk since you say that it is occurring in the winter too. Well, as much of a winter as you get in southern CA anyway.
It’s got to be a plumbing issue (cross plumbed) or that shower thermostat. It sounds like your shower and bathroom sink share the same water supply.
I would also start asking around with your neighbors in the building to see if they are having a similar problem or if it’s just your unit.
RedSwinglineOne is correct about hot water going into the cold water supply to the hot water heater. Especially, if the cold water supply runs straight down for a long distance to the heater, and if it’s a largish pipe, buoyant convection will send heated water up one side of the pipe while cold water falls down the other side. A test of this is whether using lots of hot water someplace else before you turn on the cold water tap in the bathroom will reduce or eliminate the hot water you get out of the cold water tap in the bathroom.
The pipe metal will not add much heat storage to whatever the water is already doing. The great majority of solid materials, including metals like steel and iron and copper and brass, have a volumetric heat capacity of around 1.5 or 2 million watts per cubic meter kelvin. Water has a very unusually high heat capacity of around 4 million. So, the water’s much better at holding heat, on a volume basis.
Something you haven’t mentioned yet. How big is your apartment bulding? Are we talking about a four family type building or a place that holds 400 people?
Something else you might want to do is call up your landlady when it’s acting up and make her come over and feel it with her own hand.
It’s a single bedroom place that I share with my girlfriend.
I don’t think my landlady would welcome being woken at 4:30am to come feel a pipe. She “charges extra” for service outside of normal business hours, as evinced by a threat against me to charge extra one time because I locked my keys inside the apartment at 5:30am on my way to work, sigh. She apparently forgot to do it.
Let me reword that. How many people are in your entire building? If it’s a huge 10 floor apartment complex it may take significantly longer to flush out the pipes then if it’s a small 4 family building. I’m just curious if we can rule out a few things.
Ah - it’s a two-story setup with maybe 40 spaces on each floor.
Do you know where your water heater is? IOW, have you seen the devil?
Do you know if you share one with the whole floor or if you might have a point of use unit installed somewhere?
If you share one with several neighbors you might not have the problem in your unit, it might be in your neighbors mixing valve, in the circulation pump, or somewhere else in the building.
I’m not a plumber, but is there a check valve in the cold water supply that feeds the water heater?
Also, if you share a water heater with multiple tenants one of them may have done some plumbing work in their unit without the landlord knowing. They could have screwed something up and it would take quite a while to find the problem.
You might want to contact the landlord one more time, tell her that you’ve dealt with this long enough and that you will hire the plumber to come fix this thing and then take it off next months rent.
I’m saying that I have personally exerienced this as a cause for extremely hot water coming out of the cold water faucet which was the question posed in your OP. It is just one of several reasonable possible causes suggested in this thread. Take it or leave it, the choice is yours.
To really emphasize the problem, record the taking of the temperature of water entering the toilet tank. Take the top off the tank, get a reading of the water temperature, and flush by lifting and holding the chain that lifts the flapper (connected to the flush handle by a long arm). Keep holding the chain up; if you don’t let the flapper drop, the tank won’t fill, and the water will keep running, attempting to fill the tank. Read the temperature of the incoming water, recording it as it increases. That’s sure to convince someone that there’s a serious problem.
IANAP but ISTM that hot water in the toilet bowl would have to indicate a crossed line somewhere. It sounds like your kitchen and your bathroom are served by different lines. It’s likely that they did some plumbing work a year ago that you weren’t aware of that has caused your problem. If the water temperature is around 100 degrees, a simple digital medical thermometer would suffice to provide photographic evidence.
A medical thermometer might be hard to read, but a simple digital “probe thermometer” for cooking would work just fine. One like this: Amazon.com would have a display that shows up nicely on a video camera.
All good advice …
I typed IANAP to a friend in e-mail this morning, and then read it posted here, hehe KRM
If we’re talking about using the thermometer on the toilet, I don’t think I’d want to use a medical one or a cooking one if I plan on re-using it, even if it is the top part Toilets are just too yucky for that. Maybe I’ll troll for a cheap one I can discard after I’m done.
But running the cold faucet in the shower (and I’m talking about whether the water is coming out the showerhead or the lower output) with hot water might be almost as convincing. That seems less yucky than putting something in toilet water somehow
I have a medical thermometer with a digital readout. I’ll give that a shot and see how it looks on my high def camcorder. (it’s only 720p, not 1080, but it gets the job done most times!)
As long as the cold water faucet is putting out water hotter than 90 degrees at 4:30am for more than a few minutes, we can consider that a bad thing that should be rectified, right?
I’m fairly sure that any hot water coming out of a cold tap at any time is a serious problem. It is a burn hazard.