Shower Problem - hot water for short period

Since this place always seems to know the answer I figured I'd ask about a plumbing problem. I was talking to my mom and she mentioned that over the last couple of months she's had a problem with her shower that keeps getting worse. When she's taking a shower she only gets hot water for a few minutes. If she turns on the hot water in the sink right next to the shower the water is still hot.

The shower has one knob that controls the temperature and water flow so I assumed there was something inside the control that has worn out and is biasing things towards the cold water. A quick google search confirmed this is a possibility.

My first question is does my guess make sense? Is there anything else that could cause this? My next question is how hard is it to take apart this valve and replace the parts inside (assuming the local hardware store has the parts in stock)? I redid my own bathroom 2 years ago (down to the studs) so plumbing is not an issue, but the soonest I can get over there is Christmas eve morning and both my brothers and their families will be getting there that evening and staying for a few days so I'd like to have it done before they get there. Is this something I can get done in an hour? Should I budget three or four hours? The shower is probably about 15 years old, I don't know what brand it is. I'm assuing I take the knob off, take the cover off, then take off some kind of nut or something and the valve cartridge will slide out and I simply slide a new one in, then put everything else back together.

Besides tools and a replacement part are there any other supplies I should have on hand? I'll bring some caulking, plumbers putty, teflon tape with me, is there anything else I should have on hand?

Anyone have any experience with this? If you have any suggestions, please let me know.

Thanks, Bob

My first thought was ... so I will lay out that answer anyway.

The hotwater heat element in the tank is dying.
The high temp of the water is not as high as it once was.
Meanwhile, the outside temps are getting colder and this makes the cold water even colder.

The shower knobs are being placed in "the usual" positions but the strong cold is beating out the weak hot.
Move to the sink to turn on just one temp (hot) and the hot seems hot enough.
Or, I could be completely wrong.

Tell her to shower with a Chippendale's dancer. She won't care about the water temp.

Corrosion inside the faucet partially blocking the hot feed.

If its hot everywhere else in the house, its pretty much got to be the shower faucet. Before you buy new, figure out what brand it is. A surprising number of plumbing suppliers have lifetime warranty.

It is probably a pressure-balancing faucet designed to prevent scalding when somebody flushes a toilet, and the little ball that balances the pressure is getting hung up from debris.

Your problem most likely resides in the water heater. Knowing how you make hot water would be helpful. If it is a conventional water heater, then I would first check the dip tube. It is a tube connected to the cold water supply inside the water heater that extends down to near the bottom of the water heater. As you draw hot water out of the top of the tank, cold water is added at the bottom via the dip tube. If the tube has dropped, then the cold water is added directly to the top and begins tempering the hot water in short order. Another scenario is a broken lower aquastate. Only the top of the tank will see the actual temperature the tank is set at. If you have a tankless water heater located in your boiler, then you are most likely looking at replacing the tankless coil. Whatever the case, a decent plumber should be able to figure it out quickly by running the water and seeing what happens. You would need to provide way more details to get a proper assessment here.

If the problem is at the shower only, it is the anti-scald technology gone bad inside the faucet. Even without anti-scald, those all-in-one units crap out eventually. Lowes has the replacement parts for most of them on the shelf, just pull it and take it in.

Some you cannot get to from the front and they have to be take out from behind. Often soldered in there, inside a wall. In that situation, it is easier to move.

I bet is a scald guard faucet. The faucet has a device in it to prevent overly hot water from coming out and scalding you so you look like a lobster. Basicly a bi metalic valve that restricts the hot water. It can go bad and block at too low a temperature.

Im sure you can figure out how to replace the faucet. Make sure the water heater is not turned up too high. Them older folks and kiddos can hurt them selves badly with hot water in a shower.

the shower i use every day does the same thing- but only if i take a shower in the afternoon before i go to work.. if i take a shower at 4:30 am when i get home, the water is nice and hot.. this particular shower is less than a year old- we totally redid the bathroom last January. the water heater is only 4 years old, and is hooked up for off-peak service, which means that it makes most if not all of it's hot water at night to get a cheaper rate on the electricity- which is what i think the problem is..

Thanks for the suggestions everyone. I'll start with looking at the stuff in the faucet and if that doesn't work I'll look at the hot water heater.

Bob

If the anti scald mechanism is bad, it will be bad all of the time, not after a short period of use. If it freezes in place, and you flush a toilet, you are taking away cold water pressure which will make the delivered water hotter. Hence "anti scold". The anti scold pressure balance faucets have a moving piston or ball that makes sure the pressure delivered from both hot and cold remain the same. If it changes temperature after you have been in the shower for a while, it is more likely working as it should by adjusting flow rate. Definitely sounds like a lack of hot water delivery, especially if you have a high flow shower head. Find out what kind of water heater you have and start looking there. Sounds like the water heater can't keep up with the demand for one reason or another. Don't go hacking into the valve until your sure that's the problem. There is a good chance you will break something taking it apart. Handles seize onto spindles with soap and crude, and some oddball ones are just plain hard to figure out how to take apart. Look for hidden set screws. Use a concussive force to unspin spindles. Firm steady pressure will often snap old copper tubing attached to the valves. Don't tear into it unless you are prepared to completely replace it. Remember it is inside the wall. You will need to open the wall to replace it.

pinchvalve wrote: Some you cannot get to from the front and they have to be take out from behind. Often soldered in there, inside a wall. In that situation, it is easier to move.

ROTFLMAO!

If you can't find the valve locally, take it out and soak in in vinegar for a while. Had the same thing happen to our shower, valve had got gummed up with crud from hard water.

tr8todd - thanks for the info. The part I don't get is why is it just the shower flowing cold water. The sink faucet right next to the shower will still flow hot water after the shower has stopped flowing hot water. Is it just residual hot water in the pipe going to the sink and if she let it run for longer than a minute it would be cold? I'm assuming there's one hot water pipe that goes into the bathroom but then splits with one pipe going to the shower and one going to the sink. Does the sink just flow so much less water that the hot water heater can keep up with it? She says the sink is really hot even after the shower is really cold. She has a low-flow shower head and an aerator on the sink faucet.

Of course I haven't checked it out first hand, I'm relaying info from my very non-technical mother so when she says the shower is cold it may just be that it's not warm enough to steam up the room in seconds and 'letting the sink run for a few minutes and it stays hot' could be running it for 15 seconds or something.

Thanks again for all the info.
Bob

When I had a similar problem, it was the dip tube in the water heater. But, I didn't have hot water at the adjacent faucet. Run the water in he sink longer and see if it plays out quickly. If it does, I would look back at the mixing valve in the shower.

You need to check it out first hand. Having a woman describe a plumbing problem is like having a woman describe what is wrong with her car. It gives you a good starting point where to look and that's it. Hot water issues often come down to recovery time and flow rate, especially now with all of the new wall mounted on demand water heaters. They work great at first, but I'm seeing problems with fairly new units just about every week now. The installing plumbers won't come back and service them, and told the customer that up front when they put them in. Trying to fix the them is frustrating, time consuming and expensive. Same thing goes for these super high efficient boilers. Every manufacturer has a dog in this fight now, and they are all different. Figuring out what is wrong, and where to get the replacement parts can take up a whole day of your time. And forget about fixing an intermitant problem.

I had this problem in my last apartment. Turns out the shower valve was out of adjustment.

pinchvalve wrote: If the problem is at the shower only, it is the anti-scald technology gone bad inside the faucet. Even without anti-scald, those all-in-one units crap out eventually. Lowes has the replacement parts for most of them on the shelf, just pull it and take it in. Some you cannot get to from the front and they have to be take out from behind. Often soldered in there, inside a wall. In that situation, it is easier to move.

i think he's got it right here.

same thing happened to mine. it worked well when it was first installed then gradually made the max hot setting colder and colder until i removed the safety stop entirely. though i wouldnt recommend removing it on an elderly persons shower and they may just grab the handle in a fall, bump it to full hot, and make the accident much worse......