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Question DetailsAsked on 7/16/2016

Contractor recently turned water off due to work in new bathroom. now hot water output 1-2 min then lukewarm.

this is in all faucets and shower.

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1 Answer


My first guess would be he turned off the water heater so it would not overheat or blow down steam due to lack of incoming cold water while it was turned off, and either forgot to turn it back on (could be OFF or on PILOT, or may have just turned thermostat down to low or Vacation setting). If your heater has a standing pilot, then it might heat the tank enough for there to be hot water at the very top of the tank, but not the entire tank.

If not that, then here are several other previous similar questions with different answers for different causes -

Obviously, seeing if the burner is firing (if gas or oil) when hot water is being demanded in quantity would be a first thing to check, along with the gas valve being on and thermostat set at normal setting - or with electric heater checking thermostat has not been set back and that he did not shut the power switch or breaker off. On newer units there may be a power-on light on the heater, but not on all by any means.

If the initial water is lukewarm, then thermostat or turned down to PILOT only is most likely cause. If actually HOT initially then just warm, then the dip or filler tube in the water heater corroding as noted in one of the above answers is most likely, becuase that causes cold water mixing at the top or "hot" end of the heater, whereas normally the cold water is introduced at the bottom of the tank through the dip tube so it contacts the hot crown sheet (in gas/oil units) and is heated before it gets up to the discharge at the top of the heater. If this is the case, assuming he did not do any work on the heater itself, would just be a coincidence that it happened while he was doing new bathroom work.

One other remove possibility - he made a connection mistake in the plumbing, and instead of connecting hot line to hot, he reconnected a tempered water (toilet mixing valve output) into the hot water line, causing tempered water to mix with the hot. Or in hooking up the piping he cross-connected hot and cold lines somewhere so initially you get hot water from the water heater in the hot pipes, but once water starts flowing cold water from the cross-connection mixes in and makes up about half the flow.

One other possibility, especially if a compact water system - short runs from tank to faucets - that he turned off the hot water tank valve (on one or both pipes at top of tank) either only most of the way or it leaks, so hot water is entering the pipe in static conditions, but when there is substantial flow there is not enough hot water flow to get it up to the temperature you expect. Sometimes, to test new lines, a plumber will open a shut-off valve only a bit to pressurize the lines and check for leaks - leaving it only slightlyk open so if there is a significant leak not much water comes out. Forgetting to open this valve all the way would cause low hot water flow - be it inlet valve to the tank or hot water line out of the tank.

OK - one other possibility - if your hot water system has "instant-on" hot water because of long lines or lines running through a cold crawlspace, sometimes there is a recirculating loop in the hot water piping with a circulating pump to keep hot water in the hot pipes all the time, so only the stub-ends at the faucets get "cold". During static conditions those lines, in the summer especially, might stay hot just with gravity circulation of the water if the circulating pump was turned off, but once you start pulling full flow might then run only warm at the faucet because of the flow restriction of running through a pump that is not on - check if circulating pump was turned off.

OK - I promise - I think I have exhausted all the causes I can think of. If this occurred right after he worked on the lines, his work is the obvious first suspect so get him to look at it and see if he mis-piped or left something off if the above does not clue you into the cause.

OK - I lied - one other possibility came to mind in proofing this - if he installed a tempering valve for the new bathroom toilet, maybe he caught the wrong pipes (though usually 1/2" to toilet rather than 3/4") and installed the tempering valve on the entire hot water system, not just the line to the new toilet.

Answered 3 years ago by LCD

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