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Hi, I will do my best to help solve your problem
In the shower valve, but it didn't make any difference.
Is the sink a one handle faucet as well?
Thats probably the bad cartridge to find out shut the shut off valves to both hot and cold to the sink under the cabinet then try the shower if the shower works normal then the sink cartridge needs replaced its mixing
Even when the sink faucet is off?
Yes if its a bad cartridge it can mix when off
Its easy to find out by doing how i explained
I'm not at home right now, so I'll have to try it tonight
If you shut the shut off valves under the sink then its off for sure and will take the faucet out of the picture
The water starts out hot on both the sink and shower, so does it take time to mix the hot and cold?
Yes, do you have a tank type water heater or tankless?
then its most likely a one handle faucet or could be a washing machine as well where its mixing, are you home now?
Nope, not at home
If it's mixing, wouldn't it affect other areas of the house? The master and kitchen are not a problem. Could water pressure be a problem?
Would usually show up at room where its mixing you could also have a clogged hot line, but since you say it starts out as hot then goes luke warm that's the sign of mixing
Reason I ask about the presusre is because the hot water side has a full loop that recirculates constantly.
Yes but that loop is to get you hot water faster does not effect pressure
The cold water seems to overpower the hot once the shower is turned on.
Do you have copper lines? or galv or plastic for water?
when you turn the sink valve all the way to hot is the pressure good?
When I touch the copper pipe coming into the valve, it is very hot when I first turn it on, but like the water it get colder once the water is on for a while.
Its a valve mixing it sounds like the faucet in that bathroom
presure is ok, but not as strong as the cold side.
which would be fixed with a new cartridge, bad cartridge can cause pressure drop to
One other thing I tried and it solved the problem was shuting the valve going back into the hot water heater from the hot water line.
If you hit accept we can continue with this problem on same charge for up to 30 days just try what i suggested when you get home and its probably a $20 cartridge to fix, we will not know until you try
I don't like this solution because now it takes a litte while for the water to get hot.
You killed the circ line you mean
yes, once I killed the circ line the water stayed hot in the shower and sink. It just takes a while to get hot
Its a bad cartridge. I will be on all night if your going home later to try
One you shut that sink off you should be able to leave your circle line on and check shower if its good just change the sink cartridge
Okay, I'll try that when I get home. I'm in California, so that will be several hours from now.
Thats fine i will be around another 6 hours anyway
I hope that's it because I like the instant hot water. We recently purchased this place and I didn't even know it had it until I started trying to figure out this problem
I'm sure that's going to be it, well find out
Talk to you later tonight just reply to this and i will rely back when you get back on thanks Gary
I shut off the water to the sink (both hot and cold), opened back up the circulation line and plugged the pump in. I let the pump run for a little while, ran some water in the master bathroom and kitchen.
Then I went to the shower in the guest bathroom that is having the problem. I ran a little water to get it hot. Stopped the flow, waited a minute and turned on the hot full blast. The water started out hot and then turned luke warm. Shutting off the water to the sink didn't make a difference.
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I have read what thePLUMBER has already gone over with you and as I believe he was on the right track, as soon as you shut off the recirculation line it fixed the problem with respect to the hot water being luke warm. Although you now have an issue with the hot water taking much longer to get to the faucet....am I on track so far?
With isolating the hot water recirc line, and it fixing the problem tells me that there is a problem with a check valve on the recirculation line. it is failed and is causing tempered water to enter into the piping. Typically the recirculation return to the tank enters the cold water side thus with the failed check valve, the cold water is taking the path of least resistance back into the hot water line. locate the swing check valve in the return recirculation line and change it. ]
The best way to tell if this is the problem is to locate where the recirc line return enters the cold and hold the recirc line while someone turns on the faucet...I bet that it gets cold on you...
I ran the test and you are correct. The hot water return line gets cold when the shower is running. The return line has a pump on it, but I'm not sure about the valve you mentioned. I have a few pictures, is there a way to send them and have you comment on what's there or should I bring in a plummer to install or repair the valve?
Perfect! We are on the right track... as for the pictures, you can use the paperclip icon to post them on here for me to see.
This may be what your check valve looks like...