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enter image description hereTwo plumbers and no remedies to why my hot water turns cold (but not as cold as the cold water rather slightly warmer). This problem began to happen gradually and it occurs at every hot water faucet/shower through out the house

  • Plumber No. 1: Hot water heater is fine
  • Replaced the shower (moen) faucet valves. No change
  • Turned off the recirculating pump (and ball valve before and after pump). Endless hot water but hot water pressure throughout the house is dramatically reduced -- 25 percent of the water pressure available on the cold side)
  • Plumber No. 2: Hot water heater is fine
  • Replaced the recirculating pump. No change

Plumbers are throwing their hands up so: - I also shutoff the water going to the washer and dishwasher. No change - I also turned off the water to many of the single handles sink faucets. No change

I am wondering if the significant drop in hot water pressure when the pump is turned off is an indicator as to what and try next

• I have turned the pump off (electrically) and left all valves open (recirculating and public water valves open). I get full pressure and hot water goes cold after 30 seconds.

• Turning pump on and recirculating line valves on, but close the public water valve at the tank, the water pressure slowly reduces as does the temperature (turning the shower faucet valve to cold does not increase the pressure ...just above a trickle).

• Turning fresh valve on, turning pump and valves in front and rear of pump off. Water starts at full volume and pressure reduces in less than a minute but water stays hot. Turning the shower valve to cold, the pressure gradually increases, as temperature drops, to full pressure (and then I can turn to hot and watch full pressure to reduced pressure cycle all over again.

Here is the configuration .. note three shut off valves

enter image description here

  • It sounds as if there is some restriction in the hot water supply line such that when you open a faucet the path of least resistance is through the re-circulation line, in spite of the pump, and you get a mix of some hot water and mostly cold water. I think the only way to prove this definitively would be to insert a flow indicator in the recirc line. If the flow in that line reverses when you open the hot water tap, then start looking for a restriction in the main hot line. – jwh20 May 13 at 0:07
  • Welcome to the site. Please use the edit button to update your question rather than posting answers. Posting responses as answers that need to be deleted can result in an automated lock that can prevent others from assisting you. – BMitch May 13 at 0:19
  • I can see a hose bib and attached hose. You can put the pressure measure either directly on the hose bib or likely to the end of the hose. – Fresh Codemonger May 13 at 16:19
  • I'm thinking you might have an anti-scald valve on a tub or shower and it is defective, allowing mixing of the hot and cold back through it, i.e. cold water going into the hot line. That would explain why closing the two valves didn't completely cut off pressure in the hot line. But I could be misinterpreting the facts. – J. Raefield May 13 at 20:24
  • We replaced all of the shower faucet valves(Moen 1222) to see if this was the cause. All of them changed out and this didn't fix it – Timothy Szczerbinski May 13 at 22:07
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This is quite the puzzle.

Things I noticed...

*** "Turned off the recirculating pump (and ball valve before and after pump). Endless hot water but hot water pressure throughout the house is dramatically reduced"

If you don't have a hot water circulating pump (not the recirc pump in your pictures), the hot water pressure comes from the cold water input to the water heater. This says you have a restriction in either your cold water line to the heater, after it splits off the cold water supply, or the hot water line coming out of the heater; I suspect in the hot water line or water heater itself.

*** "I have turned the pump off (electrically) and left all valves open (recirculating and public water valves open). I get full pressure and hot water goes cold after 30 seconds."

I suspect, like @jwh20, the cold water is going backwards through the recirc pump. I think the brass fitting with the white ring on the outlet side of the pump is a check valve. It should prevent the higher pressure cold water from going back through the pump, but it's either leaking or failed altogether.

It seems that the hot water line puts out enough for the recirc pump to get hot water up to the fixture, but when you turn on the fixture it draws more water than the hot side can provide. Because the cold water supply is closer to the recirc pump connection than the hot water tank is, it overpowers the hot water coming out the bottom of the tank and sends cold back through the (bad check valve and) recirc line straight to the fixture's hot side. The combination of cold water from the recirc'd "hot" line and the cold water line gives you full pressure at the fixture.

*** "Turning pump on and recirculating line valves on, but close the public water valve at the tank, the water pressure slowly reduces as does the temperature (turning the shower faucet valve to cold does not increase the pressure ...just above a trickle)."

It sounds like you have a single lever shower valve that's trying to compensate for the cold water by reducing the cold and increasing the hot but, because the supply into the water heater is shut off there's no pressure in the hot water lines.

The reason the water pressure slowly reduces is the hot water tank and the expansion tank (the large bottle-looking thing in your pictures) have air in them under pressure. As the water drains out of the water heater, the pressure drops until it's too low to push the water to the faucet.

To help isolate what's going on...

  1. As @Fresh Codemonger suggested, put a pressure guage on the hose bib (faucet) under the water heater gas valve. With the recirc pump off, recirc pump valves closed, and fixtures all off it will show you what the supply pressure is to the water heater. I would expect around 60-90 psi.

  2. Turn a fixture on full cold. From what you've described, you should get sustained full pressure at the fixture. How much does the cold supply pressure drop? I'd expect not more than about 10 psi for a shower or faucet with an aererator, more for a hose bib like an outside faucet or clothes washer. I'd still expect 40-60 psi at the water heater inlet.

  3. Have a helper switch the fixture to full hot. From what you've described, you'll get low flow but constant hot water. What is the pressure into the water heater at this point?

  4. Turn on the recirc pump valves, but not the pump, still running full hot, and I think you'll see the pressure at the fixture go up and the temperature go down as cold water flows back through the recirc line. The pressure into the water heater should be very close to what it was on #3 above, maybe a couple psi lower.

  5. Turn off the fixture. With the supply line to the heater, and both recirc pump valves, open check the pressure into the heater. Now turn on the recirc pump. The pressure should rise only slightly. That pump puts out a max of about 7.5 psi (15 ft head). If the pressure rises anywhere near this, you have a noticable restriction between the pump outlet and the fixture, probably between the water heater outlet and where it splits to the house. If the pressure drops more than a fraction of a psi you may have a blockage between the recirc pump outlet and the water heater, which I don't expect.

  6. If you have a way to check the flow coming out of the water heater, before it gets to a fixture, that would help narrow down where the restriction is. If you can't check it before the first fixture, start testing fixtures closer and closer to the heater to see if you find a point that one has full flow but the next one doesn't.

My suspicions...

How old is that water heater? Per https://www.familyhandyman.com%2Fplumbing%2Fwater-heater%2Fhow-to-repair-or-replace-defective-water-heater-dip-tubes%2F&usg=AOvVaw3z5n36r511mBdXmdLJeIMa , some water heaters, particularly those made between 1993 and 1997 may have a dip tube failure. The plastic tubes crumble and little bits of plastic get washed through the hot water lines, clogging up valves and faucets. "Often, the first four numbers on the serial number are the month and year of manufacture. If the third and fourth numbers are 93, 94, 95, 96 or 97, it could be affected."

I suspect something like this has clogged your line between the water heater and the house, and that little bits have been washed into the check valve between your recirc pump and the water heater, allowing cold water to flow backwards through it.

One way to check for this is to stop all hot water use for about 24 hours, at least overnight, then drain 5 gallons or more out of the bottom of the tank (your hose bib will do nicely) into a bucket. Let the water settle for 10-30 minutes or more and check for any plastic bits. They may be floating or on the bottom, and most any size from a grain of sand to 1/2". You may also empty the bucket through a strainer with some nylon hose to help look for them. If your heater is old and you see any of these bits, seriously look into replacing the heater. You may also have to work at flushing your hot water system and cleaning or replacing that check valve after the recirc pump.

I've run across this once with one made around 1995. It was maddening trying to backflush all the hot water lines in the house without letting the debris also flow back into the cold supply.

  • Hot Water tank was install in Aug 2013. We had the sacrificial rod looked at it was "OK" – Timothy Szczerbinski May 15 at 13:48
  • The dip tube I was thinking of is made of plastic. The sacrificial rod is different. – Eric Simpson May 16 at 10:27
  • Plumber No. 4 .. replaced the check valve and the public water pressure release valve to no avail. He decide at this point to replumb so that cold water goes in at the top and recirculating pump enters ar the bottom (they both enter at tank bottom). Even though ever had drained the tank to get the sediment out (little to nothing came out), with this new configuration, a lot of sediment was flush out and viola, hot and long lasting hot water – Timothy Szczerbinski May 17 at 22:59
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With the recirc pump off put a pressure tester on the hot water tank drain valve - see what your pressure is.

It sounds like there is something limiting the water input to the hot water tank which would cause pressure reduction. If you have full pressure cold water and 1/2 pressure hot water when your shower mixes the water depending on the type of cartridge you might only get warm water at the extreme end. With the recirc pump on it might result in it appearing like you have full pressure given you have a pump pushing the water.

  • Can you post a picture or 2 of the whole installation showing the piping to and around the tank and the cold supply? What is the model # of the pump? Can you move the camera slightly to the left for a better picture of the pump and adjacent piping? Are there check valves at each tee fitting that starts each recirc line? – d.george May 13 at 11:42
  • Plumber No. 3 was recommending re-plumbing the system into a configuration he had seen before ... given the systems has been functional for 15 years, we sent him off. Plumber no. 4 is coming tomorrow and I am armed with your recommendation. – Timothy Szczerbinski May 15 at 0:31
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    Plumber No. 4 .. replaced the check valve and the public water pressure release valve to no avail. He decide at this point to replumb so that cold water goes in at the top and recirculating pump enters ar the bottom (they both enter at tank bottom). Even though ever had drained the tank to get the sediment out (little to nothing came out), with this new configuration, a lot of sediment was flush out and viola, hot and long lasting hot water – Timothy Szczerbinski May 17 at 22:59
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Is this problem with the hot water tank a new problem or an old one. Was the hot water tank existing and upgraded with the recirc pump or is a totally new tank and recirc piping. (please, a little history). Running out of hot water in a very short time may indicate that the hot water supply out of the top of the tank could be connected to a dip tube meant for the cold water inlet. A water pressure or flow increase after opening the valves on the pump may indicate a plumbing mistake. Since the recirc line is supposed to only be connected to the hot supply at a fixture, there is no way you should get increased supply through that line. When you get the increased flow, does the recirc line turn from hot to cold or cool. It's temp should not change. After reading all the above writings, I suspect a piping and/or tank connection problem. As I just stated, you should not get increased water supply from opening the valves at the pump. A couple more things; the B&G pump you show is listed as a "cast iron pump" and should not be installed on a domestic hot water system. The pump installed should have been a brass or stainless steel pump only. The cast iron pump will degrade quickly when exposed to domestic water. The installer should have known this. If they used the wrong pump, did they use the wrong expansion tank. It should say for use on potable water systems.

  • The OP noted the problem "began to happen gradually" and now affects every hot faucet throughout the house. The pics also clearly show the cold supply come in beside the pump, through the shutoff, past the expansion tank, and into where the drain valve would normally be, not into the top of the tank. Although it worked for some time, I would call this a connection problem, just not the root cause of this issue. – Eric Simpson May 14 at 14:23
  • Plumber No. 4 .. replaced the check valve and the public water pressure release valve to no avail. He decide at this point to replumb so that cold water goes in at the top and recirculating pump enters ar the bottom (they both enter at tank bottom). Even though ever had drained the tank to get the sediment out (little to nothing came out), with this new configuration, a lot of sediment was flush out and viola, hot and long lasting hot water – Timothy Szczerbinski May 17 at 22:59

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