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Mystery: No hot water from single-handle Moen shower valve

Way2Rich's picture

I recently started fixing up a house that was remodeled about 8 years ago, and both the tub and shower use the same single-handle Moen mixing valve. You turn the shower or tub faucet on by moving the lever counterclockwise, and the farther you go, the more hot water you get.

The tub's valve works fine, but there's no hot water at all coming into the shower regardless of the lever's position. I've taken them both apart, and they appear to be the same in all respects.

I now have two questions:

1) Is it likely that the shower valve is so misadjusted that it's not letting in any hot water? Is it even possible to screw it up that badly?

2) How can I replace the valve? There are threaded connectors going into the valve itself, but it appears that they were soldered on to copper pipe with no means for unscrewing them short of cutting or desoldering the pipe. Am I overlooking something obvious or is it time to open up the wall and start cutting?

I've tried calling plumbers in on this, but everybody is too busy with heating failures right now.

Thanks in advance for any help you can provide.

The Moen's are pretty (post #207208, reply #1 of 8)

The Moen's are pretty reliable, but the most likely scenario, oddly, is that the tub valve has failed.  Single-handle units can fail in a situation where, when the valve is off, the hot and cold water halves are connected together, allowing flow through from cold to hot (or vice-versa).  Since often the cold water pipe is larger than the hot and hence has less resistance, the most likely failure mode is cold water being drawn into the hot pipe.

Rather than muck with it too much, I'd just replace the cartridge in both units, for starters.  The cartridges are readily available and fairly easy to replace (though sometimes you need a "puller").  (But note that sometimes a unit is installed "backwards" -- with the hot on the "wrong" side -- and you need to rotate the cartridge 180 degrees or some such or you'll get hot on the "cold" side and vice-versa.)

(Of course, if the setup has never, in your experience, worked right, it's possible that the plumbing was screwed up somehow during the  remodel.  Not at all unusual even for "experienced" plumbers, when they're in a hurry Friday afternoon.)


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

Rich (post #207208, reply #2 of 8)

first, don't forget to shut off both hot and cold B/4 the valve b/4 you start.

 

Remove the cartridge and replace.

 

Contact Moen and get a hot tip and perhaps the new cartridge-it should still be under warranty.

If you don't have the original paperwork, hunt up the model online (first with the style of handle/knob.  Remember too that at that time there may still have been non-pressure balanced valves still in use.  I doubt it, but it's possible.  The cartridge will maybe/probably be different for either style.

Take a picture of the face of the control, might be able to give it a name.  Moen should also be able to discern by sending them a picture email.  Or, a good plumbing supply.

No need to disconnect the rough in body (the brass thing soldered to the fittings.

 

Further, there might be shutoffs at the valve itself.  Looks like a recessed or flush screw on either side at the inlets.

Pay close attention to the orientation of that cartridge-turning them 180 will make hot/cold and the reverse.

I always put an arc of caulk behind the trim to direct any water that get's past it out and around the hole in the wall (keeping in the tub).  Leave the bottom open, so water can drain out of that small notch in the bottom of the trim.

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Pressure balance spool (post #207208, reply #3 of 8)

Way2rich:

                       Some models of Moen tub / shower valves have a device that reacts to pressure differental between the hot and cold water supply. The purpose of the pressure balance spool is to prevent scalding. This device can get stuck in a position where it will only deliver cold water.............................MikeL

                        

Mike is right on. It is the (post #207208, reply #7 of 8)

Mike is right on. It is the balancer valve in the cartridge. Moen will send you one for free if you Email them the model number or even a picture of the valve (the last one I got)

 

You can usually pull out the cartridge and soak it in some kind if solvent like mineral oil to crack it loose. To avoid the problem, turn the hot water on now and then.

Greg

You are correct, sir! (post #207208, reply #8 of 8)

All of you guys, in fact, who suggested replacing the cartridge got it right. That took care of it, and the cartridge removal tool was definitely a good idea, too.

Wish I'd known about the free option from Moen. Would have saved me about $30, although my tenant might not have appreciated the delay.

Thanks, guys! (post #207208, reply #4 of 8)

This is very helpful. I'll let you know how it turns out.

I agree that replacing the (post #207208, reply #5 of 8)

I agree that replacing the cartridge is the first thing to do. I've changed out many before. I recommend getting a genuine Moen replace cartridge and a ~$12 cartridge puller. It should have a long machine screw and a large nut mounted on a T handle. The pieces work in opposite directions to pull the cartridge out. I've never had much luck with vise-grips or anything else. The genuine Moen replacement also comes with a little package of stem grease that you can coat it with before putting the new valve in. I'm pretty sure everything is at the big box store.

It seems unlikely that the hot water never worked or it was incorrectly plumbed. I think most customers would be calling the plumber back once the tried to take a shower.

I was speculating based on (post #207208, reply #6 of 8)

I was speculating based on the possibility that the "plumber" for the remodel project was the HO.


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville