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Question DetailsAsked on 6/27/2017

Water starts out cold, gets warm for a few seconds, then goes cold again and continues that way. Problem?

Had a pipe burst in the wall, turned water off to water heater and whole house. Fixed plumbing problem, turned water back on to house and water heater. Water starts out cold then comes out warm for a few seconds and goes cold again. It just continues that way. What could be the problem?

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3 Answers


Sounds like hot water is not on - do you have hot water at ANY faucet ? The cold, then few seconds warm, then cold sounds like normal cold water, with the warm water in a section of the pipes being in a warm part of the house (so it is warmed), then back to cold and continuing cold as you then draw water which has been sitting in the underground pipes. Sounds like you did not turn the water back on somewhere, or had the water shut off at the water heater maybe.

If you have independent faucets for hot and cold somewhere in the house and water is coming out of the hot, then clearly you have water flowing. (Single handle faucets you might be getting cold water even if turned to full hot, so they are no good test). You can also test at the water heater drain valve, seeing if you have full household pressure, or just low pressure from the water standing in the tank.

Another possibility - did this repair take a number of hours so the water cooled down in the water heater, and you had turned the water heater down to PILOT or OFF, so it has not been heating ?

Otherwise, several possibilities:

1) if no water is coming out of the hot pipes but all the valves you closed are open, remotely possible a piece of dip tube or anode came dislodged and blocked up the outlet of the water heater

2) ditto to above - if no flow out of water heater, possible the backflow preventer froze up (though that is usually on entire house, not just water heater) - or if you have an expansion tank, that they installed it with an inflow regulating valve on it (only supposed to be used on boilers and such but many such tank come with it attached so he may have grabbed the wrong kind) and it froze up and is not letting water in to the water heater

3) if water comes out of hot pipes but is not heating, then water heater must be off or heating elements failed. If it is located higher than the point you drained the hot pipes from, remotely possible you might have siphoned the water out of the water heater in the course of draining the lines, it overheated, and a safety shutoff shut it down or you fried the elements (if electric) by letting them go dry.

If the above don't solve it for you, then Plumbing would be your Search the List category to find an expert to figure it out - or if this repair was done by a plumber, call him back to fix it at no additional cost to you.

Answered 1 year ago by LCD


The water to the water heater was turned off and the breaker to the water heater was off. After the repairs the water was turned back on along with the breaker. The water inside the tank is hot, we checked that by draining some. But we are not getting hot water from any faucet.

Thank you for your response. It is very much appreciated.

Answered 1 year ago by Daltonsmom


OK - this is going to get a bit complex because there are several possible causes, and two different general cases - no hot water piping flow, or hot water pipe flow but just running cold:

I am assuming a conventional water heater, not tankless - if tankless, similar measures can be taken, but add in that some have an automatic shutoff if they get limed up too much and need an acid cleaning, so check owners manual on that. Though the ones I have seen with that shut the heating off, not the outflow - but who knows what some manufacturer engineer may have thought up.

I am presuming you drained the hot water from the tank drain valve at the bottom of the tank ? So that would say the water is heating, but NOT necessarily that there is water able to flow through the tank. You did not say if water comes out from hot-only faucets (not necessarily from combined handle type which can cross-flow when there is no pressure on one side) flows. If no flow from hot side of fauceets (but cold side is working as you had indicated you have cold water at the faucets) or if single-handle faucets flow when all the way to the cold side but do not (or only a little) when turned to the hot side, then you are not getting flow through the hot water lines, so below applies - down to the ======= break below. If you ARE getting flow from hot pipe at the faucets, but it is only cold or basically cold water, then the possibilities BELOW the ===== applies.

Now - for the no flow from hot pipes case:

0) I know you said you reopened the water line valves, but double check that not only any inflow (cold side) valve was reopened and is actually in the open position, but also that if you have a happen to have shutoff valve on the hot line coming out of the tank that it is open too.

00) if the leak was in a hot line, did you by any chance use the old trick of stuffing some soft bread into the line to stop it from dripping while you soldered - in which case that break may have travelled through the line and blocked off somewhere. Varying the water pressure down and up with all faucets open on hot might break it free, as could backflushing the hot line as described below - but I would NOT let it go into the water heater - open the hot line up or open a faucet somewhere downflow of the heater to let the debris out. I have heard of cases where well-packed bread took a day or so to soften up enough to break up and travel to a faucet - and of course the more differntial pressure across it the faster one would expect it to break up, so leaving a hot faucet open (when home to monitor it) downflow of the leak spot might help.

000) (you can tell I had afterthoughts here) - if you soldered the connections at the leak, is there any chance you overused solder and actually filled the pipe up with solder (if this was a hot line that burst) ? Amateurs sometimes get way carried away on the amount of solder used and keep feeding it to a connection which is just wicking it through the joint into the pipe.

1) What I would do next - and I hate to say it because of the lost time involved, but I would definitely turn the power off to it again (or turn thermostat down to LOW or VACATiON), and let it cool off for say 4-6 hours or more (maybe overnight or while at work) so you don't risk scalding yourself during the tests. Or you could turn off the heater and drain the hot water out of the tank until it is flowing only safely warm, not hot. BUT WARNING - if you use the bottom drain AND there is no inflow coming in to the tank, that will mean it will be low on water or dry from the draining so until you prove you have water flowing through the tank again DO NOT turn the power back on until you are sure you have flow out of the tank. Hence using the relief valve per 2) below is a better tank inflow test method because it does not risk draining the tank down to the point where the heating elements can be damaged from running in air rather than water.

2) I would then, realizing there is a chance (especially if valve is older and it has not been test operated yearly) that it may stick open so best to have someone ready to shut the water to the heater off again, is exercise the pressure relief valve at the side of the water heater near the top - comes out of the side of the tank. Should have a drop tube to near the floor - lift the lever on it (with a bucket or such under the drop tube if the water would hurt anything or not go straight to a drain) and let the water flow for a good few seconds.

IF the pressure and flow rapidly drops off to zero or near zero, then your inflow is off (and any minor outflow was just the pressure in the tank from it heating up above room temp or maybe a gallon or two of backflow of the standing water out of the hot lines in the house) - meaning in that case that another valve is still closed on the cold inlet line, or a backflow preventer or expansion tank or pressure regulator which is ONLY on the water heater line (not the entire house cold line) jammed shut. It could be the shutoff valve you closed actually turned but the valve mechanism or shaft is broken inside so it did not open, or the handle is spinning on the shaft so the valve is not actually opening, or a pressure regulator/backflow preventer/expansion tank valve is stuck. You would have to (bearing in mind where the water is going to end up - usually I control it with a rag wrapped around it so it drips directly down into a harmless place or bucket), assuming threaded connections, start opening them up one by one and see where you have pressure (more than just water draining out of the house lines) and where it rapidly drops off to no flow - indicating in that case that you are on the "shut off side" of the blockage or bad valve. [When doing this sort of test I open a hose bib or faucet or such and then turn the main house shutoff valve down to the point that only a small trickle comes out of faucets or hose bibs - that way if you accidentally completely undo a fitting rather than just loosening it enough to leak good for the test you do not have a major spray on your hands.] Tracking along the system back from the heater will eventually identify the blockage point - though of course if you have soldered or badly rusted fittings you are afraid to crack open to test it gets a lot tougher and more a job for a plumber. Of course, be real careful about checking any fitting which is adjacent to or over electrical - including especially the fittings right above the tank. If you think you have water to the tank and want to check that, you probably need to shut off and drain down the cold water lines, then disconnect the union on the cold line right above the heater, and plumb in another union and 980 to divert the flow to where you can control and catch it - you do NOT want water running down into the heater housing where it may get to the heating elements.

Now - IF the relief valve (with house water shutoff valve wide open) had good steady pressure and continued high flow from it when open and pressure / flow did not drop off, then you are getting water to the heater but not beyond - meaning some valve on the outlet side is closed, or remotely possibly you have a blockage at the heater outlet itself - like a piece of plastic dip tube or anode blocking the outlet. In that latter case, (especially with electric heater) you have to shut off the inflow valve, drain the tank down a bit so it will not overflow and so the hot water pipes are drained down empty (because the blockage may not be complete so pipes may have some hot water in them), then remove the outlet piping and check for a blockage in the outlet fitting. If no blockage there, then you have to start opening up connections on the hot piping "downflow" of the heater, looking for a line blockage - which would be VERY rare but anything is possible, especially if your lines are heavily built up with mineralization or algal/bacterial growth. Or open up the hot line somewhere downflow of the heater (and control outlet to avoid wetting the tank) and then hook up a temporary connection or hose from the cold to the hot line to backflush it to try to flush out any blockage - cross-connecting one of the washer supply hoses to both the washer supply valves is an easy place to do this. You would have to control the discharge well because this should be done at full flow and pressure.


OK - now for the case where you have cold water coming out of hot faucets, or maybe a shot of warm but basically cold after that. A couple of possibilities I have run into there:

1) possible you are actually in the no-flow from heater case (possibly with a bit of hot leakage which could warm the pipes initially but not keep up with any significant flow rate), but there is a tempering valve for toilet(s) which is backflowing from cold to hot lines, so even though little or no water is coming into and/or out of the heater you still get partial or near-full cold water flow from the hot pipes located downstream of the tempering valve. This is not at all uncommon when water lines are drained - the one-way valves in the tempering valves sometimes stick open or partly open in that situation.

2) similar to 1) above, but instead of a tempering valve the plumber got lazy and hard-plumbed a tempering pipe to the toilets - instead he just linked the hot and cold lines together at a tee which then leads to the toilets - so if there is a pressure difference between hot and cold lines (like if hot line is blocked or valveoff) the water flows from the higher to lower pressure line, meaning in this case cold water flow to hot lines.

3) since you say the tank water is hot, but the water from hot faucets is cold (or warm at best) then you cannot be getting significant flow from the tank (but possibly a bit of leakage past the blockage point) - so if not tempering valve allowing cross-flow then there has to be another cross-connection between hot and cold somewhere if getting a goodly cold flow from hot lines. This could be due to an error in plumbing (though you should have noticed that at that location in the past as hot water faucet not putting out full hot water), or could be a mixing type valve (single-handle) which is allowing water to flow from cold through to the hot side in the valve, or possibly a cross-connection at some other device using tempered water. If this is the case, it is likely that the cold flow from hot faucets will be less than full flow volume, if it is bleeding through interior to a valve or mixing valve. If this is happening, it still means there is a blockage in the hot lines somewhere on the "downstream" side of the heater or the heater inlet or outlet is blocked, so you are still back to the first case of no flow from the heater to the faucets.

4) very rare but happens sometimes when people put in a point-of-use water heater or hot tub or dishwasher or such on the hot line only and have higher water pressure than it is supposed to take - check for a pressure regulator on the hot line only ("downstream" of the heater) which might have locked up when the water pressure dropped to zero when the water was shut off. Sometimes they freeze up, a few of the mopre positive shutdown brands tend to drop to zero pressure and have to be readjusted back up to desired operating pressure after a water line shutoff.

OK - I am pretty much burned out of viable possibilities - so if the above was too confusing or did not solve it, time for a Plumbing contractor (your Search the List category to find well-rated and reviewed contractor to track it down. Of course, the better you can isolate the issue or rule out certain cases the less time (and money) he has to spend figuring it out.

Answered 1 year ago by LCD

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