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The house has four bedrooms. The 40 gallon gas water heater is about 60 feet from this shower. The house is a one story house in flat terrain. I have already changed the mixing faucet for the shower, using a new Moen faucet. It does the same, the problem was not solved. The house has hot water everywhere (kitchen, dishwasher, washer, and in all the fixtures of the other three bathrooms). In the last bathroom (65 feet from the water heater) there is hot water in the sink, but no hot water in the shower. What can cause this problem?

I already have spent a lot of money on several plumbers that just could not make it work. I desperately need your help, please, any thoughts? If you need more information please request it.

Update: I discover that when the water is running cold from the hot water at the max., if I open the cold water in sink of the same farthest bathroom, the water in the shower start coming warm, for a minute or so then it continues cold. Does this give a hint to diagnosing the problem?

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Is there flow from the hot water but it's cold, or is the shower cold because there is only water being supplied from the cold water supply? –  Steven Feb 22 '13 at 1:59
    
When you replaced the faucet, did you clean the lines of debris? –  Jason Feb 22 '13 at 2:08
    
This is mike the one with the litle hot water for a few seconds hower problem. STEVEN: Thank you much for your help. One plummber and assistant did this test. Assistant was in the underfloor, plummber was maneuvering the fawcet. Before turning on the valve assistant has one hand in the hot incoming pipe and other hand in the incoming cold pipe. He was suppouse to tell when the pipes got hot or cold. When started the lever was turned from the cold to the hot, to the max hot. Assistant repoted the hot pipe is hot but getting cold it passed 5 seconds and then he said both pipes are cold now. MONS –  user11715 Feb 22 '13 at 5:13
    
I'd be interested to know what's actually coming out of the pipe as far as pressure and temp - holding it might not be a great test. the pipe could be warm because some portion of it is near a heating duct –  Steven Feb 22 '13 at 13:06
    
Mike, to merge your duplicate accounts, follow the steps here –  BMitch Feb 23 '13 at 23:56

2 Answers 2

Modern shower faucets are pressure balanced to prevent scalding by limiting hot water if the cold supply loses pressure (say, if someone flushes the toilet)

If this mechanism jambs, it would limit hot water.

One test is to shut off only the cold water to the valve... repeat test, hot only -do you get any flow in either case?

Some mixing valves have "built in" stops that let you service the cartridge without shutting off the whole house. if so, turn both setscrews fully CCW to open.

The cartridge should be removed and the valve body inspected to make sure a valve seat isn't blocked.

With the cartridge out, slowly turn on the hot only (hold bucket in front of valve and have helper ready to turn off hot valve). Does it get hot? If so, problem is in cartrige. If not, problem in pipes

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Were you able to try any of my suggestions related to removing the cartrige? What were the results? –  HerrBag Feb 25 '13 at 14:27
    
This was posted as an anonymous edit: Dear Mr. Herbbag: I do appreciate very much your help with your answer. One of the Plummers that I called he was sure that the problem was in the shower valve. He replaced the existing by a new Moen shower fawcet. It did not correct the problem. Then He tested by doing what you prescribed above, and the problem continues. May be the problem is in the pipes. Mr Herbagg I value very much your opinion, If you can suggest something more I will appreciate very much. Thank you! –  Niall C. Feb 28 '13 at 21:15

Your water supplies may be pre-mixing. That is, mixing cold and hot water even when no faucet is on. This may happen if you have any fixture where hot and cold water handles/valves are left on but a third valve that is used to regulate flow and is shut off. You, or a previous owner, might have made this configuration so that the temperature never has to be adjusted at that fixture, for example. The hot and cold water may be mixing in the short length of pipe/faucet behind the third valve. This reservoir of mixed water then begins to extend out into the supply pipes. If so, you might get this pre-mixed, warmish water from a second fixture nearby, even when you only turn on the cold water at this second fixture. After a few seconds, the pre-mixed water is flushed out of the cold water supply pipe and pure cold water comes out the faucet. This may explain the initial burst of warm water from the shower.

Edit: To (hopefully) illustrate the above pre-mixing scenario, imagine this. You have hot and cold supply pipes leading to your bathroom. Each junction, one leg going to your tub+shower and one going to your sink (ignore the toilet for a minute). The sink's hot supply goes to the hot faucet handle. The sink's cold supply goes to the cold faucet handle. Nothing hinky there. Now imagine the hot and cold supply goes to a tub with its own hot and cold faucet handles. One old tub fixture I've seen had two additional valves (in addition to the two from the faucet handles). One to control the flow of the tub faucet and another to control the flow of a shower head. Now let's say both the tub and shower flow valves are turned off so no water is flowing but the cold and hot water faucet handles/valves are turned on and left in position so that the mix/temperature doesn't have to be adjusted. What may happen in this case is that the hot and cold water supplies become connected and open to one another in that little length of pipe that sits between the hot/cold faucet handles and the tub+shower valves. So the hot water slowly bleeds into the cold supply and vice versa. After some time the warmish water in the cold water supply spreads back to the supply's junction and then further down the pipes toward the sink faucet. Then when you turn on the sink's cold water the first burst is warm rather than cold, all because there is a wonky fixture configuration somewhere nearby that opens the cold and warm supplies to one another. Now this particular configuration is old and probably very rare (and poorly designed... and don't wrack your brain too much trying to visualize this faucet/valve figure, just the idea of pre-mixing) and it doesn't describe your configuration but I mention it just as a possible clue to follow. Check nearby fixtures and appliances (laundry?) that may be either misconfigured in such a way to broken and thus pre-mixing the hot and cold water even when the fixture/appliance is not on/running.

As for why the shower ultimately produces cold water when the handle is turned to hot, it almost sounds like the hot water supply is connected to the cold stem on the back of the shower flow/temp adjustment valve, and the cold supply connected to the hot stem. Try leaving the shower valve adjusted to cold for a while and see if the water gets warmer. Also verify that the connections at the back of the valve are not reversed.

Also, try to collect more details on when the hot water pipe gets warm and gets cold. If the hot water pipe between the shower faucet/valve and the nearest junction is ever getting hot that suggests that hot water is actually flowing through the faucet. If it gets cold when the faucet is on that suggests that the cold water pressure is overwhelming the hot and pushing its way through the shower mixer into the hot supply pipe.

Hope some of this helps.

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See a rejected suggested edit for some feedback from the OP. –  Niall C. Feb 28 '13 at 22:24
    
Added edit per feedback from OP. –  jlpp Mar 1 '13 at 15:14

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