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Robert Lamoureux: The mystery of the mix-it valve

Posted: December 24, 2011 1:55 a.m.
Updated: December 24, 2011 1:55 a.m.

Hi Robert,

I have a very unusual situation in my home that has been happening off and on for the last two months.  Sometimes, I get hot water when I turn on the cold water on my bathroom faucet, and this morning, I had hot water in my toilet. I could actually feel the heat when I sat down. What is going on?

Jean M.


Hi Jean,

The bottom line is you have a mix-it valve somewhere in the house, probably in the bathroom.  

A mix-it valve is a single shower handle. Instead of having a hot and a cold control you have one that sits in the middle. Generally they pull out and turn to the left or right.

Inside the mechanism there is a diaphragm with a small plunger. The rubber plunger will sometimes rot. There is also a small metal plate inside the hub that can rust through. If you have either one of these problems, it will cause the hot and cold water to mix on its own. 

For the repair, you would first shut the water off to the house. Or, if once you remove the handle and the escutcheon plate, you might have a couple of set screws that will allow you to turn the water on and off.  You have to be really careful with the set screws to make sure they’re working. If they are frozen, then they are unusable. 

Once the water is off, you will need to take the cartridge assembly apart. Look to see if the packing is damaged, and if so, it will also need to be replaced. Take it all to a plumbing supply to make sure you purchase the proper replacement. There will be identifying marks on the cartridge to install it right side up. 

When turning the water back on, be sure to do so very slowly. This should resolve your problem.  


Hi Robert,

I live in a condo complex. I have low water pressure and the association is telling me this is my responsibility. How can this be? I have five faucets and two of them are bad. Why is this my responsibility? Thanks,

CiCi B.


Hi CiCi,

If three of your faucets are working properly and you have adequate pressure everywhere else, then the pressure regulating valve is doing it’s job. If all of your fixtures had problems, then replacement of the PRV would probably be an HOA responsibility.

Since you have two fixtures that aren’t working properly, it could be you’ve got a steel braided supply line with broken interior rubber that is causing an obstruction. This is not uncommon and is a homeowner responsibility. 

You could have a plugged angle stop or it could be the fixture itself that is obstructed. It is a coincidence that you have two of them, doing the same thing at the same time, but it happens. These also belong to the homeowner.

So with only two bad fixtures, it would fall back on you. The repair is only a matter of troubleshooting.  Start by shutting off your angle stop and disconnect the supply line to the faucet. Have a bucket under the sink. Turn on the angle stop and see if the water is strong. If so, you know the problem is in the fixture. If not, then the problem must be with the angle stop or supply line. 

To replace an angle stop, you have to turn the water off or you will have a flood in your unit. If you don’t have an individual shut off valve to your unit, you’ll have to valve down the building. You may want to call a qualified plumber in at this point.        


Hey Robert,

About six years ago, I had my house re-piped. I have to admit that he was the cheapest one, so it seemed like a good deal at the time, but not too good of a deal now. I’ve got leaks in the ceiling and a wall. I have his original invoice that shows that the work was paid in full, but the phone number no longer works. Do I have any recourse or way to get reimbursed for these repairs? Thank you,



Hi B.C.

The cheapest way usually turns out to be the most expensive in the end. It sounds like either inferior copper was used or maybe the joints were soldered poorly, or both. 

You have no recourse. If he’s out of business or can’t be found, there’s nothing that can be done. I know that cheap sometimes looks pretty good to some people, but I recommend to get three different bids on the big jobs.

If one of the companies is substantially lower than the other two, then a warning light should go off telling you there’s something wrong. 

I’ve found over the years that these cheap guys can only last so long before these types of situations catch up to them. They go out of business because they can’t afford the litigation. Carriers will decline them.

As I’ve said before, don’t hire just anybody off of the street. Go with a reputable, experienced and licensed contractor. Get referrals and recommendations. Check with the California State License Board. Find out everything you can about somebody before you give them any money and invite them into your home.   



I’m on our homeowners’ association board of directors, and we have a ground fault indicator, or GFI, that trips on the sump pumps during rain. We have to go out in the middle of the night to reset it. We’ve covered it with plastic and replaced it, but it keeps tripping. What do we do?

Oleg U.


Hi Oleg,

What you should do is remove the GFI. Although it’s in a wet location, it does not require a GFI because it’s a mechanical pump that is only to be touched by a trained professional. 

Usually, you do want to install GFI’s at wet locations. In this instance though, it will only continue to trip due to the outside humidity and/or rain.

So take it out and have an electrician hardwire it directly.  You will also need to install an inline service switch so that the service person can turn it off to work on the pump if necessary. 

Everyone who sends in a question answered in this column will be given a full-color, limited edition The Signal/Your Home Improvements T-shirt. The shirt is available for pick up at IMS Construction in Valencia.

Robert Lamoureux has 25 years experience as a general contractor, with separate licenses in electrical and plumbing contacting. He owns IMS Construction Inc. in Valencia. His opinions are his own, and not necessarily those of The Signal. Opinions expressed in this column are not meant to replace the recommendations of a qualified contractor, after that contractor has made a thorough visual inspection. Send your questions to


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