High water pressure - intermittent

[exj625]

I have a strange problem.
Normally my water pressure remains around 65 psig (checked it using a guage on a hosebib outside).

Intermittently, however, it will go up; way up, to the point that the faucets show noticable resistance to turning on the bathroom or kitchen. After opening the faucet and allowing the pressure blow itself off, it remains normal.

It's been happening for a year or so, infrequently, and recently has increased. I put the guage on yesterday, and I noticed it again as I started to turn the faucet this morning, so before I turned the water on I went out to check it and it was 150psig.

Over the past few weeks I have also noticed that it seems to happen more consistently after running the shower. (i.e. take a shower for 10-15 min, shut off the water, then see high pressure at the sink which blows off and then all is normal)

Before I go calling in the plumber or installing a pressure regulator, is there something that could be causing this? or could it be a water company problem? I checked with my neighbor, and they haven't noticed anything odd.

Thanks for any ideas.

 

[SteveW]

I'm assuming you are not on a well.

You probably have "thermal expansion" if your water pressure goes up markedly after using a "batch" of hot water. This happens in water systems which are "closed," meaning that you have a one-way check valve in your supply. This commonly happens at water meters and pressure-reducing valves. Basically, when the water heater is heating up a volume of cold water, that water expands. If the pressure can't go back into the water main, then pressure inside your house pipes goes up markedly.

The solution is installation of an expansion tank.

Do a search on this forum on "thermal expansion" and you'll see some other recent posts on this.

 

[Sponsor]

 

[exj625]

Thanks, Steve. I hadn't correlated the symptom to use of hot water, but I'll do some experiments and pay attention to that.

We have city water, and no pressure-reducing valve. I had assumed our system was 'open', but it sounds like you're suggesting the water meter out near the road may have a check valve, which would prevent the expansion to push back into the water main?

I have a backflow preventer that isolates our sprinkler system, but that branches off before the water enters the house. But, to eliminate it as a variable I'll turn it off, as it's winter anyway.

 

[SteveW]

That's right - modern water meters do have integrated check valves, to prevent potentially contaminated water from one person's home from getting into the general supply. If you have a meter with a check valve, you would have a closed system and yes, then the heated, expanded water can't push back into the water main.

Pressure-reducing valves act as check valves - but by your first post doesn't sound like you have one - right? They are kind of bell-shaped brass contraptions that would be on your water supply downstream of the meter.

A good experiment to confirm the theory of thermal expansion is to see what your standard water pressure is on the gauge, then run the hot water for 5 minutes or so to partially deplete the water heater (5-10 gallons will do), then shut off the hot water faucet and watch the gauge closely for the next 10 minutes, making sure no water will be running (no one flushes a toilet or turns on a faucet; washing machine not running; no ice maker cycling). If you have thermal expansion, the pressure will go up dramatically, usually well over 100 psi. This is due to the volume of cold water expanding as it is heated. If you then open any faucet in the house, hot or cold, even for a second or two, the pressure will come right down. Time for an expansion tank - a 5-gallon tank with a rubber bladder, half filled with water, half filled with pressurized air.

 

[Runs with Bison]

Yep, sounds like typical thermal expansion. You can confirm with a $10 test gauge (with a peak reading indicator) from a hardware/big box store.

Many PRV's don't act as check valves. In fact, many have pressure relief built into them (back into the supply.) However, this relief doesn't work if the supply pressure is high enough or if there is some other form of check in the system--as mentioned previously.

PRV is a confusing abbreviation since in the process industry it means "pressure relief valve." PSV is also used: pressure safety valve.

 

[nor1313]

Sounds like the same problem that I'm having. Strange, I've been in the same house for 26 years and it just started about two months ago. My system does have a Watts regulator off the supply that I replaced myself after 16 years in the house because the water pressure was constantly above 140. That was about 10 years ago.

My question is, what would have caused this problem to surface now after all these years? Nothing has changed in the house or at the street.

Thanks in advance.

ron

 

[SteveW]

Sounds like the same problem that I'm having. Strange, I've been in the same house for 26 years and it just started about two months ago. My system does have a Watts regulator off the supply that I replaced myself after 16 years in the house because the water pressure was constantly above 140. That was about 10 years ago.

My question is, what would have caused this problem to surface now after all these years? Nothing has changed in the house or at the street.

Thanks in advance.

ron

1. Has something changed in the way you use hot water? The only time thermal expansion shows up is when your WH has to heat a slug of cold water, AND no one turns on a tap (hot or cold) for a while. Has someone in the home started to take long showers right before bed, so no one uses any water for a while after that person uses a big bolus of hot water? etc. etc.

2. Have you recently replaced toilets, or fill valves in toilets? Old, slightly leaky fill valves will sometimes let off the excess pressure so you aren't aware of thermal expansion.