Mixet shower valve leaking

[babbo]

The tenant broke the handle off an old Mixet shower valve. No big deal, and since the cartridge was at least thirty years old I decided to replace it too. Got the long pre-1968 cartridge and installed it without any problem but it leaks a bit: drops falling from shower head about once a minute. (The old valve didn't leak, btw).

What's the remedy? Many thanks.

 

[All Shore Plumbing NY]

The tenant broke the handle off an old Mixet shower valve. No big deal, and since the cartridge was at least thirty years old I decided to replace it too. Got the long pre-1968 cartridge and installed it without any problem but it leaks a bit: drops falling from shower head about once a minute. (The old valve didn't leak, btw).

What's the remedy? Many thanks.

A slow drip right after installing a new cartridge usually points to one of three things, cartridge not fully seated, worn seats/springs inside the valve body, or an aftermarket cartridge that's slightly off spec.
Since the old one didn't leak, I'd pull it back out and check for debris, damaged rubber seats, or improper seating. Mixet aftermarket parts can be hit or miss even when installed perfectly.
Did the replacement come with new seats and springs, or just the cartridge?

 

[Sponsor]

 

[Sylvan]

Google works wonders

If your Mixet valve is leaking, hard to turn, or failing to shut off entirely, you typically need to replace the internal cartridge (usually model MS5AT or MS4). [1, 2, 3, 4, 5]

Key Components and Features

• The Cartridge: Mixet cartridges are non-pressure balancing and feature a design where the hot and cold water mix as the stem is pulled outward and rotated. [1, 2]
• Trim Kits: The exterior handles and faceplates usually come in clear acrylic, chrome, or brushed nickel and are broadly interchangeable across Mixet systems. [1, 2, 3, 4, 5]

Common Mixet Shower Valve Issues
Mixet valves are prone to a few recognizable quirks over time:

• Leaking or Dripping: Over years of use, the rubber seals on the cartridge degrade, causing the shower head or tub spout to drip. [1, 2, 3]
• Handles Turning Together: Sometimes, the outer trim plate and the inner temperature knob rub against each other, causing both to rotate at the same time. This is usually an installation issue that can be fixed by adjusting the depth of the brass base and shaft on the cartridge. [1]
• Difficulty Adjusting Temperature: Hard water scale buildup inside the valve body can seize the cartridge, making it very stiff to operate.

 

[babbo]

A slow drip right after installing a new cartridge usually points to one of three things, cartridge not fully seated, worn seats/springs inside the valve body, or an aftermarket cartridge that's slightly off spec.
Since the old one didn't leak, I'd pull it back out and check for debris, damaged rubber seats, or improper seating. Mixet aftermarket parts can be hit or miss even when installed perfectly.
Did the replacement come with new seats and springs, or just the cartridge?

Just the cartridge. There was no trace of a spring with the old one and I'm not sure how such would work. Replacement cartridge was pre 1968 model.

 

[Jeff H Young]

Ive worked on mixit a fair amount mixit esentially is old school stem the washer is a normal 00 flat washer and the "seat " is integral fixed part of the valve you might want to take a real good look in the valve body. you might be able to reface the seat , and get it working smooth again. i wonder if a bevel washer might work ? never tried to use a bevel washer when seat was beat up

 

[All Shore Plumbing NY]

Just the cartridge. There was no trace of a spring with the old one and I'm not sure how such would work. Replacement cartridge was pre 1968 model.

Got it — then I'd lean toward the new cartridge itself not sealing perfectly in the old valve body. That's unfortunately pretty common with some aftermarket Mixet cartridges.
Might be worth pulling it back out and lightly cleaning the sealing surface inside the valve body in case there's mineral buildup preventing a full seal.
If that doesn't fix it, the valve body itself may just be too worn to seal reliably with a new cartridge at this point.

 

[Jeff H Young]

Just the cartridge. There was no trace of a spring with the old one and I'm not sure how such would work. Replacement cartridge was pre 1968 model.

Ive worked on these many many times befor like I said Its the washer or the seat most likely its the seat as yours is the long pre 68 model youll probebly wind up replacing the valve but if you try refacing the seat or a beveled washer ( ive never tried one on a mixet ) it might help a cheap refacing tool can be found also the washer size is 00 thats all the advice there is really that I know of . but you gotta take it apart again and look inside with a light hope this makes sence its super easy