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Rick, Construction Supervisor
Category: Plumbing
Satisfied Customers: 21374
Experience:  Licensed Master plumber with 40+ yrs. experience.
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My shower starts out hot but then after 4-5 minutes goes cold,

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My shower starts out hot but then after 4-5 minutes goes cold, then 4-5 minutes later gets hot again. Had this problem 4 years ago and I put in a new shower head and it worked. Now it is back. It doesn't happen every time though. Tried a new shower head again but no luck. What should I do next?


does the hot water stop at any other fixture during this time that the shower gets cold? If it does we need to do some things to check your water heater, if it doesn't and it is just this one fixture, then we need to check it out. So some questions, any idea as to the brand or model the shower valve is? Single handle, Two, or Three Handle? About how old is it? If you try to increase the hot water when it is running cold, does it get hot or just stay cold?

Customer: replied 4 years ago.
Kohler, single handle. This is the only fixture tha gets cold. Also, turning the handle does not change the temperature once it goes cold.
I will do my best to help with your problem

What type of water heater do you have?
Customer: replied 4 years ago.
Rinnai Tankless Water heater. Every other fixture/faucet in the house runs perfectly fine. This is a problem with the shower itself.
There is nothing in a single handle Kohler shower valve that would explain what you describe unless it's a thermostatic valve. While it is (remotely) possible that it's a problem with the valve it's much more likely the problem is related to the Rinnai. None of the other faucets in the house have the same flow rate as the shower so they are not good indicators of the source of the problem. You could verify that the Rinnai is the source of the problem by letting the shower run and watching the Rinnai. If you have hot water at first then lose it the Rinnai burner should fire up at first then shut down at about the same time you lose the hot water in the shower. One other way to check the Rinnai would be to touch the hot water line out of the heater when you lose the hot water in the shower. It's also possible the Rinnai has mineral deposits in the heat exchanger that are the cause of your problem and need to be flushed out.
You could replace the cartridge in the shower valve since that is the only internal mechanism in the valve that has any likelihood at being the source of a water temp problem but unless it's a thermostatic valve I doubt replacing it would solve the problem.
Customer: replied 4 years ago.
Thanks. we have two other showers in the house (same Kohler single handle) that work fine. Does that fact change your answer that it would be the valve? is that the same as a stem?
Yes that changes my assessment. If your other showers work fine then it can only be in the valve. A single control valve has it's working mechanism incorporated in the cartridge. It's only similarity to a stem is that it's connected to the handle. You would need to know the model of the valve (not the trim) in order to get the right cartridge. If you do replace the cartridge yourself be sure to flush out the valve before reinstalling the cartridge. You do this by turning the water back on with the cartridge removed. Unless there are integral shut offs in the valve (screwdriver slots on a short stem where the water lines connect) this takes 2 people. One to turn the water on and off and the other to make sure the water stays in the shower. There is a slim chance that the problem could be due to a faulty intergral shutoff as well. The shut off stem can be removed and checked for a loose washer or some other obstrcution
Customer: replied 4 years ago.
Thanks - last question - should any plumber be able to fix this?
Yes any plumber should be able to fix this.
Rick, Construction Supervisor
Category: Plumbing
Satisfied Customers: 21374
Experience: Licensed Master plumber with 40+ yrs. experience.
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