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turtle_rouge 06-21-2010 11:21 AM

Fixed Toilet, now high water pressure?
I recently replaced the parts inside of our toilet tank. It had been running ever so slightly since we bought the house. Now that the toilet is not leaking, our faucets occasionally have a moderate burst of pressure when they are first turned on and then they go back to their normal flow. What is going on?

woodchuck 06-21-2010 09:04 PM

Sounds like air in the water line and it settles at the highest points which are the faucets. Could be from work on the water line down the road etc. It takes a long time to get it all out sometime.

Redwood 06-22-2010 07:19 AM

My guess is that you have a Pressure Reducing Valve that has failed or, a Thermal Expansion Tank on a water heater that has failed...

The leaking toilet bled off the excess pressure...

Nestor_Kelebay 06-22-2010 09:47 AM

My guess would be that your water meter has been replaced by your local municipality.

You see, older water meters used to allow for backflow through the water meter. So, when cold water was heated in the water heater, the expansion of the water would result in a tiny bit of back flow through the water meter.

However, there's been a great effort to prevent this kind of backflow because it could result in "Grey" water getting back into the water distribution system and coming out somewhere else, like into your glass of drinking water. So, nowadays all water meters have check valves that prevent that backflow.

So, if you don't have an expansion tank on your water supply piping, that burst of pressure is probably just due to the expansion of cold water in your water heater.

So, probably best to take a hammer to them new parts in your toilet tank until the toilet leaks again. ;)

As Redwood says, the problem was always there, it's just that the leaking toilet bled off that pressure.

turtle_rouge 06-22-2010 09:55 AM

Those are the two things I was worried about, Redwood. That was all I could find out from Google and I was just hoping it wasn't true.

I looked at the hotwater heater yesterday. The pressure relief valve appears to be working fine. I think.... It moves up and down. There is a tube attached to it that goes off behind the water heater. I have no idea what it connects to. I am hoping it drains somewhere other than the floor...

I also looked for a pressure reducing valve and couldn't find one. There wasn't one just off the meter at the street. And, our water shut off is apparently outside, buried under 6 inches of dirt. I dug it up and didn't find anything past the knob. I'm not saying there isn't one, I was just only willing to dig so deep into that stupid little hole with my plastic spoon at that moment... I am guessing it is a bad thing that my main water shut off is buried outside (Is this normal? Do we need to dig it up and insulate it with something easier to remove than dirt?).

Is there a way I can tell for sure if it is the hot water heater or the elusive pressure reducing valve instead?

turtle_rouge 06-22-2010 10:01 AM

Ah, Nestor, you are probably correct. Our water meter was replaced about 6 months ago (yes, sadly, the toilet had been leaking that long...).

So, do we need to install an expansion tank or is it okay? It is not a huge rush of water, just 1-2 seconds of an increase in volume. I am guessing if we are going to be out for any amount of time, it would be a good idea to let a faucet drip. But, for just daily use, is it alright to have a little pressure build? And, why is the pressure relief valve in the hotwater tank not taking care of this?

turtle_rouge 06-22-2010 10:09 AM

Okay, awesome! I just looked up the expansion tank. I can totally install that. Whew! I am so glad that it is not a more major problem.

I am still wondering though, probably a stupid question, but why does the pressure relief valve not take care of this problem?

handyguys 06-22-2010 12:37 PM

The T&P valve is to prevent catastrophic failure of the water heater. Yes, that pipe probably just goes to the floor, best case into a pump pit or floor drain. The expansion tank essentially eases out the pressure fluctuations. Here are a couple pictures.

Redwood 06-22-2010 02:42 PM

If the new water meter has a check valve it creates a closed system where the thermal expansion of water being heated in the water heater will create a high pressure burst.

If you let off the high pressure burst and the water heater is not reheating then later check to see if the burst is still present it will answer some questions.

If the burst is not present then it is thermal expansion....

If it is present then there is probably a PRV hidden somewhere that has failed...

In either case you still will want an expansion tank.
If you are installing the expansion tank in a horizontal position like the ones shown in the picture posted by Handy Guys make sure the tank is supported. At some point the bladder in the tank will fail and the tank will become waterlogged. When it does the tank will be quite heavy and require support to keep it from breaking off.

Nestor_Kelebay 06-23-2010 12:20 AM

Turtle Rouge:

Another thought...

Another thing to note is whether or not your PRV has a large brass knurled or hex nut on the bottom. On the PRV's on hot water heating systems, there will typically be a brass or stainless strainer screen in the PRV that can be replaced by removing that large knurled or hex nut. (And, it's NORMAL for newbie homeowners to start fiddling with the pressure setting on their PRV when it's not maintaining the heating system pressure only to discover that the problem was a clogged strainer screen.)

What's crossing my mind is that if your PRV has a clogged strainer screen, then the "burst of pressure" you're experiencing may be what the pressure in your water supply system should normally be, and the lower pressure afterwards may simply be due to the lower flow rate through a partially clogged strainer screen.

For example, if you look at this Watts pressure reducing valve:

The cutaway view below reveals that the knurled knob on the upstream end of the PRV is there to allow removal of the strainer screen for cleaning. All the water flows through that strainer screen before flowing through the PRV and into your house. My personal experience has been that most of the problems I have with leaking faucets is the result of sand and hard dirt like metal filings in the water coming into the building. If your PRV has a strainer on it, (and I expect it should) then I'd also expect that screen would need to be cleaned periodically. It's common for hot water heating sytem PRV's to have their screens clog up, so I would expect the same thing from the PRV on a house's water supply piping.

Also, here's what I consider to be a good idea...

On the pressure reducing valve to my hot water heating system boiler, within 2 feet downstream of that PRV I have both a tee with a pressure gauge and a ball valve with a drain on it on the upstream side. That arrangement allows me to close the ball valve and adjust the setting of the PRV very quickly and accurately because the 2 feet of pipe downstream of the PRV pressures up very quickly as water flows into it. Once I adjust the PRV to the correct pressure with the ball valve closed, I can open the ball valve and have confidence that the whole heating system will be filled to that same pressure over the next few hours or so. That's why I set it up like that.

If you have a PRV on your house's water supply piping, you might want to put the same kind of piping in place. That would let you check to see what pressure the PRV is set at, and whether or not it's maintaining that pressure when you open a faucet.

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