Author Topic: Water Heater going intermittently cold?  (Read 8339 times)

Miss Growing Green

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Water Heater going intermittently cold?
« on: May 27, 2014, 09:17:38 AM »
Last night we were doing some plumbing work- using PEX to pipe a new bathtub and tie it in to our existing lines, so we shut off both the hot and cold water, piped everything, and since last night the hot water has been running intermittently cold.

As in, it will run hot for 30 seconds, then a blast of cold, then luke warm, all within the span of a couple minutes.

Is it a coincidence that this happened right after we shut the water off and messed with the plumbing?  Hard to believe!  What could be causing this?

The water heater is electric and less than 1 year old- standard tank style.  We tried reseting the power to it at the breaker and running the hot for a while, listening, and confirming the heater was indeed turning on and heating, and it is.

Any suggestions?  Thanks guys!

EDIT: For clarification, this is happening at all spigots- not just one (kitchen sink, bathroom sink, tub, and shower), on both two-handle and one-handle type faucets.
« Last Edit: May 27, 2014, 09:58:07 AM by Miss Growing Green »

phred

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Re: Water Heater going intermittently cold?
« Reply #1 on: May 27, 2014, 12:10:04 PM »
I once saw something similar to this on Ask This Old House.  There was something wrong with the mixing valve for the tub/shower.  Because of that, the sinks only had cold water.  Unfortunately, I don't remember the details.

Another possibility: when you shut off the water to the hot water heater (?), did you also turn off the electric power feed to it?  Heating elements heating air soon destroy themselves

Miss Growing Green

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Re: Water Heater going intermittently cold?
« Reply #2 on: May 27, 2014, 01:35:59 PM »
Magnum- are you saying that if there is something wrong with one of the mixing valves in the shower the whole house would have intermittent hot and cold water?

To answer your question- no, when we shut of the water to the hot water we did not also shut off the electricity.  However, we did not drain the hot water tank, so the tank shouldn't have been heat "air only".  We also had the water off for maybe 30 minutes max.

Greg

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Re: Water Heater going intermittently cold?
« Reply #3 on: May 27, 2014, 01:40:19 PM »
What fixtures get the mixed water?  Are you certain you have the hot and cold correct at the tub?  Were they correct before your work? 

Is the tub valve shut, and not just the shower head?  I can imagine that if you shut water off at the showerhead but the mixing valve was still on, it would draw through the valve this way and that, depending on what fixture it was and how close it is to the tub.

On some valves, if the hot and cold are backwards, you can "fix" it by removing the valve cartridge and turning upside-down, and then reinstalling it.

Miss Growing Green

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Re: Water Heater going intermittently cold?
« Reply #4 on: May 27, 2014, 02:03:19 PM »
Greg:
We have one walk-in shower that gets "mixed" water, as well as our kitchen sink. (by "mixed water" I am assuming you mean a one-handle faucet?)

We also have a separate whirlpool bathtub and 3 different sinks that all have a separate handle for hot and for cold water.

ALL of the faucets in our whole house have this problem now, and they are scattered over 2 bathrooms and a kitchen.

It seems like it is a problem with the water heater and not an individual fixture, since it is affecting all the fixtures.

Greg

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Re: Water Heater going intermittently cold?
« Reply #5 on: May 27, 2014, 02:14:14 PM »
I can't think of a way an electric tank style water heater could do this on its own.  Can you isolate (shut off) the supply lines to the tub you worked on?  This will show you if it's related or not.

Miss Growing Green

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Re: Water Heater going intermittently cold?
« Reply #6 on: May 27, 2014, 03:58:28 PM »
Not really... we just tied the tub's hot and cold into the main lines.  Nothing branches from the tub to another fixture, and the tub doesn't have a specialty valve or anything- it's just a roman tub faucet with a hot and cold spigot.  I don't see how the tub could be causing this...

phred

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Re: Water Heater going intermittently cold?
« Reply #7 on: May 27, 2014, 06:11:53 PM »
well, can you remove the new lines you installed and see if the rest of the plumbing reverts to normal?

Rezdent

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Re: Water Heater going intermittently cold?
« Reply #8 on: May 27, 2014, 07:30:57 PM »
How hard is the water in your area?
When was the last time the water heater was drained and cleaned?
We have beastly hard water here.  In past repairs we've stirred up enough chunks in the water that they'd get in the pipes, collecting in a bend or such and block the flow.  Turn water off, chunks settled back down the pipe and water would go.  At least till the chunks all got caught again.  We drained and cleaned the tank.  The other thing that comes to mind could be that the elements are going out.  These can be repaired on lots of water heaters.

big_owl

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Re: Water Heater going intermittently cold?
« Reply #9 on: May 27, 2014, 08:23:50 PM »
I don't see how it could be due to the water heater element if it is a tanked water heater and the water is only intermittently going cold.  The tank should be a large source of hot water, so if the water in the tank is all homogeneous and hot at some point then you can't just get a slug of cold water without it being due to a valve somewhere allowing a slug of cold water to mix in.  Maybe if something was broken with the plumbing inside the heater which caused the new cold water entering the heater to port into the heater outlet before it had a chance to mix fully with the hot water in the tank... but I don't even know how you'd diagnose that.  Have you tried just draining the tank directly to see if the problem happens on water taken directly off the tank?

Ziggurat

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Re: Water Heater going intermittently cold?
« Reply #10 on: May 27, 2014, 08:40:27 PM »
We have had a problem with water quickly going intermediate temperature, but perhaps not such big fluctuations as you described.  The research turned up the dip tube as likely culprit:  see e.g. http://www.waterheaterleakinginfo.com/how-to-replace-the-dip-tube/

But that would be quite the coincidence because that should have no relationship with the work you did.

phred

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Re: Water Heater going intermittently cold?
« Reply #11 on: May 28, 2014, 05:12:44 AM »
Interesting comment on the dip tube.

My first two guesses are:
1) With the new plumbing run, a cold water "pipe" is feeding into the hot water side.  I wonder if there existed a hot water return line, and they tapped into this?  Removing the new lines -- plug, cap off, whatever -- may give a clue

2) The mixing valve in the new tub faucet is installed upside down or 180 degrees off, thereby changing the entire water "flowchart".