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I'm noticing reduced hot water pressure (on all faucets/shower) after significant hot water use (2 long showers, 2 loads of HE (High Efficiency) laundry, and using a sink for about 5 minutes). Cold water pressure is normal.

Is this hot water reduced pressure normal, or indicative of a problem?

Note that this reduced hot water pressure is a new thing. It was not an issue in the past.

The water heater is a Rheem natural gas tank-type storage water heater, with a capacity of 40 gallons.

UPDATE #1: I visually inspected the exterior of the water heater, and there are no visual defects. There is no water around it, either.

UPDATE #2: When I looked at the water heater, it has not two, but three pipes attached to the top. I found this QA, but I'm not sure if the answer applies. One of the three pipes is not insulated, so I'll assume that's the cold water intake. Both of the other pipes have insulation on them, so I'm guessing hot water is coming out of them. But I don't know why there are two of those pipes. There is no solar (I wish), reservoir, or instant-on hot water. If it helps, the hot water heater is a Rheem PowerVent 2.

UPDATE #3: I'm hoping (and thinking) this is irrelevant, but I figure the more information I include, the better you can help me. When I visually inspected the exterior of the water heater, I heard what I thought was a dripping sound that began about 10 seconds after the unit turned on. I diligently searched for water, but I found none. If my ears were working correctly, it seemed that the sound was coming from the horizontal CO vent pipe that leads outside. I don't recall it ever making such a sound, but I never stood around and listened so intently. I don't know if this means anything, and I don't want to divert attention to a red herring, but I thought it was worth mentioning.

UPDATE #4: The hot water pressure has been different since this event took place.

  • Sometimes, it is normal: I can put any faucet on full-hot and the water comes out with normal strong force.

  • Other times it starts off with a strong force and then, after running for 5-10 seconds, the pressure decreases to about 30%. It then stays at that pressure while I let it run. If I turn off the sink, and then turn it back on, the same thing happens (full pressure followed by a reduction in pressure).

Note that these things happen regardless of which faucet I use, and do not seem to be dependent on water use before the test.

  • You might want to check that the cold water supply valve to the water heater is fully open. – Dan D. Feb 28 '16 at 6:55
  • @DanD. My apologies. Your suggestion is an excellent one, but I accidentally omitted an essential fact: that this is a brand new issue. I will edit the question to reflect this important detail. – RockPaperLizard Feb 28 '16 at 9:55
  • Strange problem since a tank style water heater is essentially a straight pipe with a big holding tank. Pressure and flow should be the same regardless of water temperature. Even with the heater turned off you should get full flow of cold water through the tank. If all these faucets are pressure balanced (the shower definitely should be) I would start looking for your problem there. – ArchonOSX Feb 28 '16 at 10:09
  • @ArchonOSX I'm sure the shower is pressure-balanced because I put a new valve in myself about a year or two ago. I think each faucet is individually pressure balanced. But why would the all the pressure-balanced valves (at least 5 of them) fail at the same time? – RockPaperLizard Feb 28 '16 at 10:59
  • They are supposed to reduce hot water flow proportional to the cold water. So, if the cold is shut off they are supposed to shut off to prevent scalding. If the cold is restricted, your hot would reduce flow proportionately. That is why Dan D. said to check your cold water valve to make sure it is fully open. If you have a utility sink with faucets that are not pressure balanced, check the hot and cold water flow there. Are you on a well? If you run the cold water continuous does the pressure drop after long use? Maybe your well pump can't keep up. – ArchonOSX Feb 28 '16 at 11:38
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New Answer Derived From Exhausting Initial Answer & more:

It's your Water Heater, here are some things to try in determining whether or not there's actually a problem.

1 - Drain & clean the tank properly. ONLY do it when the pressure's good. Turn off the Hot & Cold Water & WH, open the T&P valve & drain the tank (see manual) to somewhere that contents can be seen. Blast on the cold water when you can start to "slightly" rock the tank to stir & break things up & periodically continue this until it's empty. Operate the hose bib handle to crush any big particles or Poke into your fully open hose bib if the hose flow drops. Then, when empty blast on the cold water & let drain & repeat until nothing comes out. Then, do just a 2-minute fill & drain & blast again to get all remnants out.

2- Check your status lights to your manual for detected problems.

3- Status Lights will also indicate a problem with the heater's Gas Control valve. But, this could also be a Gas Meter response to a run-away or leak detector, improbable since flow-rate wouldn't have changed.

4 - This is a pretty cutting edge unit you have & everything's interconnected. The fan & burner won't outrun each other & there may even be a Water Exit Regulator involved to turn the heater, sort of, into a Tankless Water Heater.

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Original / Initial Wrong Answer: If you have a Hot Water Recirculating Pump somewhere else, you're driving its thermostat batty & it's only now showing signs of needing attention. It would be stealing pressure until it's reading hot water again. You may have noticed the pressure returns after 10 to 30-minutes, when the Water Heater has recovered enough or recovered fully.

  • Thanks Iggy. I don't see one. It's not reasonable for a builder to put one inside of the walls is it? – RockPaperLizard Feb 28 '16 at 10:54
  • Well, it was worth a shot. And, not that I know of. BUT, & another, IF you have any boxes that hide the plumbing it could be back there...kudos to the plumber for pulling that off. – Iggy Feb 28 '16 at 10:58
  • Thanks. No boxes hiding anything, but the pipes go straight from the water heater into the walls and then come out at the fixtures in other rooms. There are almost no visible pipes. There is a fan mounted on top of the water heater to blow the exhaust outside. They never integrate a hot water recirculating pump into one of those, do they? – RockPaperLizard Feb 28 '16 at 11:03
  • Nope, you're good on the CO fan. But, I'll give the pump one last IF you have a crawlspace the pump would finally be found there. The pump idea is tapped-out, pun intended, after this...unless you're lying & you have pumps everywhere. – Iggy Feb 28 '16 at 11:08
  • LOL... had to look under my chair to make sure I wasn't sitting on one! Nope, no crawl space. This is quite the mystery. – RockPaperLizard Feb 28 '16 at 11:18

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