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Question DetailsAsked on 11/29/2015

Master Bath shower runs when ANY hot water faucet is turned on...cold turns it off. Cartridge already replaced 3x.

We have a tankless water heater. We initially replaced the cartridge in the shower faucet (single lever) because it was becoming more and more difficult to regulate the water temperature. After replacing the cartridge, the shower dripped incessantly so the plumber replaced with a different cartridge....and then a 3rd. The drip was fixed. But now the shower turns on fully but ONLY when hot water runs from any other faucet in the condo....washer, kitchen, 2nd bath, disihwasher, kitchen sink. If I switch on the cold water so that both hot and cold are on, the shower stops running.

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2 Answers


You did not say what brand and model - that makes it tough to answer intelligently.

I would have to guess, from the other faucet use factor (meaning only works with decreased pressure in hot lines) and stops when cold is turned on, i would guess either the cartridge is installed upside down (some can be), or the temperature control setting is set all the way to the cold setting or limit - so the cartridge limiter (sounds like this is a self-regulating type, designed to maintain constant temperature even as the incoming water cools down as the water heater starts recharging) is shutting down the flow - either because the limit screw/knob is set all the way cold, or because the hot and cold sides are swapped so you confused the heck out of its brain !

Guess it could also be the wrong model cartridge - again.

Depending on brand, I guess it is also possible that the lever itself was installed off-center, so what you think is turning on to full cold is actually off, etc. Might just need to have lever taken off and replaced correctly on the shaft - if this is a shaft that allows more than one installation setting. Some are oval to prevent more than one position, some round or splined or octagonal so have many angles of rotation they can be installed at.

I would say, after 3 - no now 4 attempts coming up, maybe you need to get a refund from the first plumber for all but the final cartridge itself (if it turns out to be the correct one - else for that too), and find a plumber who knows how to install and adjust unitized self-regulating cartridge shower control valves.

And after all is said and done,undoubtedly time for an appropriate Review on AL.

Answered 4 years ago by LCD


I may have failed you when I first answered - depending on the type of cartridge, it is possible you have excessive water pressure, so the pressure in the system is ramming the cartridge full off UNLESS hot water is drawn at another point to reduce the pressure at the shower. When you turn on the cold, that would introduce the cold water pressure at the cartridge also, thus pushing it closed again.

Easy thing to check - buy a thread-on pressure gage with hose thread for about $10 and put it on any hose-threaded faucet in the house EXCEPT ones on a steam or hydronic heating system - those are low pressure. Outside hose bib (be sure to rewinterize if applicable), washer connections, drain on hot water heater (watch out you do not spray and burn yourself) are likely connection points.

Household pressure should definitely not be over 70 psi and generally not over 50 - you would have to check manufacturer literature (probably in instructions for cartridges) on maximum operating pressure for the valve, but if over about 50 psi I would suspect this as a possible cause.

Another thing to check - so I actually missed on two p[ossible causes for you - it may be your control valve is working right, but if you have an adjustable spray head like a Waterpik or such, or especially if a handheld spray nozzle, the valves in them usually work in a piston mode, so the valve liming up or getting stuck can cause this sort of behavior. Carefully unscrew the head (without turning the pipe coming out of the wall) and see if the water flows correctly with the shower head off - if so, that is the problem, and usually better and cheaper to replace than try to fix.

Sorry - when I first answered must have been late at night so the old gray matter was not fully functioning.

Answered 4 years ago by LCD

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