Woke up this morning and heard a dripping from the shower. There was some dripping even though the knob was off. I messed with it for a second and the dripping stopped. Then I turned the water on for real and noticed something strange: If you turn the knob towards cold the water comes out but if you turn it towards hot the flow reduces until you get all the way to the left at which point there is no flow at all.

I checked every other tap in the house and they all get hot water. I did a Google for this problem but found people (on this board) whose showers were only getting lukewarm. Mine
Is a case of nothing coming out of the hot side at all.

The knob is one of those plastic things that looks like a fake crystal. Could the problem be there? Nothing looks out of the ordinary to my sleepy eyes.

Ideas?

One possibility is that mineral buildup in the heater has entered your hot water pipes and got sucked up into your shower valve where it's now blocking the hot water inlet ports. The solution to this is to shut the water off and open up the valve. If your faucet's a Delta thyen check and clean the seats and springs, if other then the inlet ports on the cartridge. Before you reassemb the valve turn on the hot water to flush out the hot water supply. If mineral build up in the heater caused this let me show you how to flush your heater. For long life and fewer troubles you should keep your heater clear of mineral build-up by flushing on a regular schedule. Attach a hose to the boiler drain at the bottom of the tank. With the pressure on, open the boiler drain and let it run until the water runs clear. You will see a spurt of red,(rust) followed by white grains,(lime or calcium carbonate). This shouldn't take more then a few minutes. Do this monthly to keep it clear. Now flush out your hot water lines on ALL fixtures. Now pull each aerator and clean the screens. Be sure you put them back togather the same way you took them out. Don't forget to flush it out every month. Your heater will thank you for it. Hope this helps, Tom

Thanks for the detailed reply. It does help... It makes me want to call a plumber! I recently took apart and fixed my washing machine but something about messing with the plumbing gives me the heebie jeebies, especially since that might not be the problem.

It was wicked cold here last night and I'm afraid the pipe might have frozen. How likely is it that the hot water pipe in the shower would have frozen but not the cold water pipe in the same shower and not the sink in the same bathroom or any other pipe as far as I can tell?

If it's not possible that it's a frozen pipe then maybe I should try what you suggested... although I'm definitely nervous about it!

If you can give me a brand name and its age I can walk you through it. Sounds like a Delta from your description. Regards, Tom

I'm getting a rash of complaints about hot water pipes freezing up. If the problem doesn't go away after it warms up then I can walk you through flushing your valve if you can give me the brand name and the age of the valve. Regards, Tom

Thanks for all the suggestions. It is a Delta fairly similar to this: http://www.absolutehome.com/assets/images/product/13240.jpg

I've removed the knob and the metal plate so I can see into the wall. There's a lot of cold air rushing out. The thing that's annoying is that I have no access to anything, really. I tried blowing a hair dryer in for a few minutes to see if maybe something would thaw out but have had no luck yet. When I turn on the hot water it's not like something is rattling or trying to come out. Nothing happens at all. What should I try?

Thanks for all your help!

I talked to Delta and they suggested changing the seats and springs too. I'm not too handy but I did fix my washing machine recently (as I already mentioned) so maybe I should give this a shot.

One thing I'm not sure about: There's a knob on the pipe leading to my water heater that was labelled as the "water main" and there's a pipe out by the front of the houses that was labelled "water heater supply" but I feel like the labels are flipped. Here are photos of the labels:
http://buskerdog.com/wp/wp-content/uploads/2007/02/watervalvesquestion.jpg

(I edited the URL. Should work now.)

As you can see, the tag on the pipe going straight into the hot water heater has "Water Main" punched while the pipe in the front of the house says "water heater supply". The plumber who put those there knew what he was doing but now looking at it it doesn't make sense to me. If I want to turn off the water to remove the old shower mechanism should I turn off the one that's LABELED water main (i.e. the knob directly hooked into the hot water heater) or the one labeled "water heater supply" that's up at the front of the house or both?

If you can wait for warmer weather to see if it's a frozen pipe. The shut off at the front of the house is the house shut off that shuts down everything while the one near the heater shuts off the hot water. What is it that you wish to do. Wait for warmer weather or tear into the valve? Regards, Tom

I kind of want to give it a shot since it's our only shower and I don't know when it's going to warm up.

Should I be replacing the entire apparatus or just the seat and springs? I just called my local hardware store and they have seat-and-springs replacements for $1.50 or the whole shindig for $12. Either way, better than service call.

Most Delta shower valves are constructed like this, (see image). Turn the water off and open up the valve. Remove the seats and springs,(#7) and turn the water back on for a few seconds to see if the supplies are clear. I'm still not too sure you have to change or replace anything. If the shower valve worked before then it should still be working when you clear the seats. Let me know if you get a strong stream out of the open valve when you pop some water to it. Regards, Tom

Great! Thanks for that.

And just to clarify on the image I linked of my pipes, I'm going to turn the water off in the second picture, right? The one labeled "Water Heater Supply" but that seems to be the actual main supply. Right?

I'm going to
1) shut off the water by the front of the house
2) remove shower knob apparatus
3) turn water back on and hope that obstructions flush out
4) turn water back off
5) replace knob apparatus
6) turn water back on
7) bled all radiators and run all sinks etc...

If I'm wrong about any of this let me know!

Great! Thanks for that.

And just to clarify on the image I linked of my pipes, I'm going to turn the water off in the second picture, right? The one labeled "Water Heater Supply" but that seems to be the actual main supply. Right?

I'm going to
1) shut off the water by the front of the house
2) remove shower knob apparatus
3) turn water back on and hope that obstructions flush out
4) turn water back off
5) replace knob apparatus
6) turn water back on
7) bled all radiators and run all sinks etc...

If I'm wrong about any of this let me know!

Just to clarify on the image I linked of my pipes, I'm going to turn the water off in the second picture, right? The one labeled "Water Heater Supply" but that seems to be the actual main supply. Right?
Correct
1) check
2) check, And check for trash around the seats and springs.
3) check, If no water comes out then the pipes may be froze up.
4) check, after a few seconds, there should be a strong stream
5) Check
6) check,
7) Why would you bleed the radators or run the sinks? Please explain.

Good luck, Tom

I guess there's no need to do that. Woops.

Just got back from the plumbing supply store and got some new parts to put in. I'm not going to attempt just yet because I don't have anyone handy to be in the bathroom and holler if something goes awry when I turn off the water. But the one thing I did think of is if I can follow the pipes back from the bathroom through the basement ceiling and find shut off valves closer to the bathroom, rather than the main shut off for the house, I should use those, right? Localizing the work is better if possible. Because I think I can locate something a little more local than the main.

Some tub and shower valves have screwdriver stops in the valve body. The can be found, if they are there, by removing the handle, face plate and looking at each supply at they point it connects to the valve. Simply turn the screwdriver stop clockwise to shut the valve off. Good luck, tom

Well I'm mighty annoyed. I finally got the extra set of hands needed to try this whole mess out. We turned off the water just to the bathroom, removed all the parts of the shower knob, and turned the water back on. Whoopee! Water flow craziness! But wait, that water feels awful cold. Let's try just turning on the hot for a second to see if it's even coming out. Nope.

So there's no hot water coming out of the shower PIPES at all, even though the same bathroom knob controls the sink and it gets hot water. So there is a problem between where the shower and sink split off, which I guess is in the floor or wall or something. Arg! Well, I guess I'll let the plumber take a look at it tomorrow and go out a lot of money. Unless there's something I should still be checking, but I'm at a loss of what it is. Any suggestions are welcome.

At least I gave it the old college try!