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Old 12-05-2008, 10:51 PM   #1
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Low Hot Water Pressure

We've traditionally had great hot water pressure, but over the last few weeks we've experienced lower hot water pressure (the cold has always been fine). The city did some work up from my house last weekend and after that the hot water pressure got much worse throughout the entire house (the cold is still fine).

I live in a 13yr old split foyer and own a gas hot water heater. I drained the tank and the water came out perfectly clear, so my initial thoughts are that I don't have sediment in my hot water pipes. I took apart the cold water valve for my hot water heater and it "appeared" to be fine (however, I don't think it turns the cold water completely off when I close it, so I still suspect that might have something to do with it).

I called the city to check the incoming pressure and they said it was great (110 psi).

In any of the 3 bathrooms, if I turn on only the hot water in the shower and then turn on the hot water in the sink, the pressure in the shower drops quite a bit. What's crazy is that if I leave the hot water on in the shower and the hot water in the sink, but also turn on the cold water in the sink, the water pressure in the shower gets strong again (almost stronger than when I only had the hot water in the shower on).

When I showed this to the city personnel, they were baffled. How would turning on the cold water in the sink (while also running hot in the sink), help my hot water pressure in the shower?

Any ideas on my problems??? Thanks in advance to anyone that replies.


Last edited by btennant; 12-05-2008 at 10:53 PM. Reason: typo
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Old 12-06-2008, 01:34 AM   #2
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Was anything asked or said about possible air in your lines ?


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Old 12-06-2008, 02:13 AM   #3
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Turning on the cold water will pressurize the hot water in your hot water piping. The hot water will come out of the shower head with greater pressure for a while, until the cold water starts to mix with the hot water, causing the temperature of your shower to drop.

Look on your water heater for two "thick pipes" above the water heater. If it is a high efficiency water heater, those thick pipes are check valves. The cold water inlet has a check valve with a ball in it made of polypropylene (which floats). That valve prevents hot water from rising up the cold water inlet line and cold water from spilling into the water heater. The hot water outlet line has a nylon ball in it (which sinks) and prevents the hot water in the water heater from rising up into the distribution piping, and the cooled down water in that piping from spilling back into the water heater. Maybe try giving them both a good shake to loosen up any dirt that's causing those plastic balls from moving.

It could be that one of your check valves is stuck closed cuz of dirt in it.

It could also be that one of the ball valves, either inlet or outlet to your water heater is partially closed.

Buy a small pressure gauge and connect it to your water heater's drain valve. Measure the pressure. Now connect it to the spout on your laundry room sink, and turn the hot water on. You should record the same pressure. Now, start your washing machine on "whites" so that the washer starts filling with hot water and see if the pressure gauge on the faucet spout drops. If so, then the blockage is somewhere upstream of the laundry room tub faucet.

Crude as it may sound, solving problems like this is just a matter of doggedly tracking down where the pressure drop is occuring. It's just as simple and as hard as that.

Also remember that a restriction to flow is only going to cause a pressure drop when there is flow. When there isn't any flow, the pressure throughout the hot water distribution piping will be what it should be everywhere. So, you need to measure the pressure in the hot water pipe WHILE there's flow through that pipe. It doesn't matter WHERE you measure the pressure; as long as it's downstream of the flow restriction, you'll see a drop in pressure when water is flowing.

Last edited by Nestor_Kelebay; 12-06-2008 at 02:18 AM.
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Old 12-06-2008, 06:16 PM   #4
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remove all the airaters on the showers and sinks check for fine sediment.the reason the hot shower increases when you turn the cold on in the sink is the cold water(higher) pressure is checking the hot water pressure(lower) into the sink mixer.water seeks the easier path of resistant and with that it goes over to boost the hot/shower.
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Old 12-09-2008, 09:31 PM   #5
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Thanks for the info.

The city sent someone from their Building Maintenance dept and they cut the pipe that runs out of the hot water heater. Sure enough, it was clogged big time with calcium, which they said was very common in our city.

The pressure is as good as it's ever been.

Thanks again.
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