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Rick
Rick, Construction Supervisor
Category: Plumbing
Satisfied Customers: 21370
Experience:  Licensed Master plumber with 40+ yrs. experience.
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We have a tankless hot water heater. In the shower in the master

Resolved Question:

We have a tankless hot water heater. In the shower in the master bedroom, the water gets hot, then cold in the middle of the shower. If you turn up the handle to hottest setting, it recovers, but can take up to a minute. We have tested and can have hot water running in the bathroom sink at the same time it is cold in the shower.

The shower handle is a single handled Moen. The house is 14 years old. The people who installed the tankless hot water heater think it is a water volume issue, they say the pressure is OK. They are not plumbing specialists. Could something on the Moen handle be bad?
this does not happen every time - maybe every 3-4 showers.
Submitted: 5 years ago.
Category: Plumbing
Expert:  Rick replied 5 years ago.

Rick the plumber :

Welcome to Just Answer, I will do my best to help with your problem

Rick the plumber :

Is sounds like you have a problem with the pressure balancing cartridge in the Moen shower valve. If there was a problem with the water heater then you shouldn't have hot water at the sink at the same time you have cold water in the shower. You probably need to replace the cratridge in the valve

Customer:

That makes sense to me. thanks/

Rick the plumber :

You're welcome

Rick and other Plumbing Specialists are ready to help you
Customer: replied 5 years ago.
One more thing - should we just replace the whole faucet or just the pressure balance cartidge - and how much do you think this should cost (a range?)
Expert:  Rick replied 5 years ago.
I wouldn't replace the whole valve (faucet) just for this problem. If you have some other additional reason for replacing the valve then this could be a good time. It could cost a couple hundred to fix this depending on the cost of the part and if the plumber has to make 2 trips because the part has to be ordered. A new basic valve with standard trim (no designer trim) installed typically costs ~$450 installed in the Boston area. If there is no access to the wall behind the valve then a cover plate can be used and all the work can be done from the shower side. The cover plate looks like this and allows for a hole large enough to work through.
Customer: replied 5 years ago.
Thanks, that's helpful.
Expert:  Rick replied 5 years ago.
You're welcome