I have a new home with a pressure regulator. When set at 50 psi the flow at all locations is very weak. When set higher the flow is acceptable. The plumber says it must be set at 50psi. The flow at this setting is much weaker than normal (normal being virtually any other location, our last home, public restrooms, other homes, etc. etc.) At what pressure can I safely set the system?

I have a new home with a pressure regulator. When set at 50 psi the flow at all locations is very weak. When set higher the flow is acceptable. The plumber says it must be set at 50psi. The flow at this setting is much weaker than normal (normal being virtually any other location, our last home, public restrooms, other homes, etc., etc.) At what pressure can I safely set the system?

How are you testing it to show it is set at 50PSI?

Is there a gauge on the Pressure Reducing Valve -- Or are you pressure testing with a gauge elsewhere?

How are you testing it to show it is set at 50PSI?

Is there a gauge on the Pressure Reducing Valve -- Or are you pressure testing with a gauge elsewhere?

There is a tempory gauge on the hot water heater drain faucet. It has a tell-tale that shows the maximum pressure as the plumbing company wanted to check for pressure spikes. In the last 3 days it has been as high as 65 psi, typcially 50 psi and as low as 40 psi. The reason the plumbing company is checking this is that the water heater pressure relief valve is leaking. It is the third pressure relief valve installed. I think it is leaking is due to too high water pressure as one of my "friends" adjusted the pressure reducing valve without a gauge and I subsequently found the water pressure was well in excess of 100psi. Good news, nothing blew up or leaked, except the pressure relief valve on the water heater. Water flow was good, better than good I guess. Until now the plumbing company has changed the pressure relief valve without checking the pressure, even though I asked them to.

There is a tempory guage on the hot water heater drain faucet. It has a tell-tale that shows the maximum pressure as the plumbing company wanted to check for pressure spikes. In the last 3 days it has been as high as 65 psi, typcially 50 psi and as low as 40 psi. The reason the plumbing comapny is checking this is that the water heater pressure relief valve is leaking. It is the third pressure relief valve installed. I think it is leaking is due to too high water pressure as one of my "friends" adjusted the pressure reducing valve without a guage and I subsequently found the water pressure was well in excess of 100psi. Good news, nothing blew up or leaked, except the pressure relief valve on the water heater. Water flow was good, better than good I guess. Until now the plumbing company has changed the pressure relief valve without checking the pressure, even though I asked them to.

Testing pressure at the HW Tank is not going to give you an accurate reading -- Thermal expansion is going to give you a reading of +/- 10 PSI.

BTW, 50 to 65 PSI, if deliverable, is the recommended pressure for a residential potable water supply system.

Does your system have a back flow preventer, and if so, do you have an expansion tank on the hot water heater? When you add cold water to the hot water tank on each hot water draw, it then expands. If the additional volume isn't free to go out the inlet, PRV, water meter, and anything else between the hot water heater and the city line, the pressure will go up through out the system until something gives. Usually it is relief valve. They are cleverly set below the pressure rating for all the other components. I fail to understand how you could have a 10 psi. differential between the water tank and PRV with an open 3/4'' pipe connecting them and no flow. In a connected system, the fluid will flow to equalize the pressure everywhere in the system.

I fail to understand how you could have a 10 psi. differential between the water tank and PRV with an open 3/4'' pipe connecting them and no flow. In a connected system, the fluid will flow to equalize the pressure everywhere in the system.

I'm pretty sure we've had this discussion before, Labman -- If the tank is fitted with one way inlet and outlet nipples, as most newer tanks are, the pressure built up by thermal expansion will not flow back through the cold side of the system.

Getting back to the OP. I see 3 problems.

1 The relief valve leaking due to a back flow preventer and no expansion tank.

2 Low water flow due to construction debris somewhere in the system. %0 psi. should be plenty.

3 A plumbing company not seeing and correcting the above. I do admit that a few years ago it took Tom and I a while to catch on to needing expansion tanks with the back flow preventers. As more and more public systems add them, it seems to me that practicing plumbers should have caught on to them by now.

It is ludicrous to think those little plastic flaps are going to hold much pressure. I still have the nipples that came with the water heater I installed last year. I just tried blowing through them. I can easily blow through them in both directions. Since Tom says you don't need dielectric unions, I had thrown them in my junk box without looking at them. With some of the posts I am seeing here, that may be the best place for them.

They may slow down little convection cells saving a certain amount of energy, but I wonder how much? I do have the pipes insulated on my tank.

If you have water flowing when you measure pressure, it is going to be lower the further from the source and closer to the outlet. Otherwise, when no water is flowing, the pressure will be the same everywhere in the system, little plastic flaps or not.

Having looked at the professionally installed tank at my church, I certainly hope Tom is right about not needing dielectric unions. Oh yes, it has 1'' ones coming directly out of the 60 gallon tank. Then there are 1'' X 3/4'' galvanized reducing couplings that the 3/4'' copper pipe adapters screw into.

I am assuming by pressure regulator you mean a pressure reducing valve.
If it is, it means the pressure from the street is higher than is allowed by the plumbing code.
Find out what the plumbing code allows in your area. Mine is between 40 and 80 PSI but many houses go up to 100PSI.
PRV's have a built in backflow valve, this allows water to flow in one direction. If you have a gauge on your water system past the PRV take the pressure as soon as you shut off the water at a tap.
If everything is tight(no leaks) the pressure will start to rise from thermal expansion from the hot tank.
Often quite dramatically, enough to cause the pressure releif valve to release at the hot tank.
You can purchase an small surge fixture that will take up the expansion. They are sold more to stop water hammer but will work for both. Only a few dollars at a plumbing supply store.
Then set the pressure as high as you want in the house.
65-70 PSI is what I find people are most happy with.
Good luck

Getting back to the OP. I see 3 problems.

1 The relief valve leaking due to a back flow preventer and no expansion tank.

Well, we don't know if that is the case because he han't responded to your earlier query.

BTW, you may or may not know this, but the requirement for backflow prevention is a State/Municipality requirement, not a code requirement under any of the varying codes adopted throughout the country.

The city of Seattle doesn't require them, but if you drive across the bridge into Bellevue you'll definitely need one.

If he does have a backflow preventer on his system, then a malfunctioning check on his double check, or the remote possibility of both checks malfunctioning would certainly explain the surging and the failure of the T&P's.


2 Low water flow due to construction debris somewhere in the system. %0 psi. should be plenty.

Construction debris is always a possibility -- And if he has a backflow preventer installed without an inline wye strainer, then debris may be lodged in the seat(s) of his backflow preventer -- If the municipality is going to require backflow prevention, then they should also mandate protection for the backflow preventer in the form of a wye strainer -- But of course the don't.


3 A plumbing company not seeing and correcting the above. I do admit that a few years ago it took Tom and I a while to catch on to needing expansion tanks with the back flow preventers. As more and more public systems add them, it seems to me that practicing plumbers should have caught on to them by now.

The problem is that Plumbers are only required to know the letter of the code when sitting for their competency exam -- Understanding the 'WHY', IOW, the engineering behind the 'WHY' never enters into the equation.

I do the best I can in the code compliance classes I teach, but 2 hours a night twice a week for six weeks leaves a lot of questions unanswered -- They know what a vacuum breaker is and when one is required, but have no idea whatsoever what it does.

Also, the municipalities requiring backflow prevention haven't thoroughly thought through the requirement -- Most of the municipalities simply require a double back check, which offers no relief whatsoever for the domestic side of the equation.

A much better device for protecting both sides of the equation would be a Reduced Pressure Backflow Preventer -- This device would protect both sides without causing surging and pressure buildup on the domestic side.


It is ludicrous to think those little plastic flaps are going to hold much pressure. I still have the nipples that came with the water heater I installed last year. I just tried blowing through them. I can easily blow through them in both directions. Since Tom says you don't need dielectric unions, I had thrown them in my junk box without looking at them. With some of the posts I am seeing here, that may be the best place for them.

Well, there's the rub, there are a number of different manufacturer specific heat trap nipples, and there are a number of different ways of manufacturing them.

The kind you speak of, with hinged plastic flaps are only one example.

Some use machined seats and machined balls matched to the seats and rely solely on pressure and back pressure, while others use machined seats and balls and springs to return them to the seats.

If it weren't a warranty issue, as it so often is, I would yank them out and throw them in the trash -- But it isn't in my best interest to invalidate the warranties of the fixtures and appliances I provide and install.


They may slow down little convection cells saving a certain amount of energy, but I wonder how much? I do have the pipes insulated on my tank.

Frankly, I think they're crap -- But part of my success and my longevity in the trade is based on not invalidating the warranties of the fixtures and appliances I provide.

Not sure what growler's problem is. Maybe he spilled coffee on his lap and is a bad mood.
From what you said in your original post my advice is accurate and correct.
I have been a trouble shooter in a large municipality for 27 years and have come across this problem many times.
The trouble with plumbing terminology is that different terms have different meaning all over the country.
I would rather use a generic term that you can use at a plumbing supply store.
I don't know how to post a link but if you Google water hammer you can see what a water hammer arrester looks like.
This will cure the problem if water expansion is causing your pressure relief valve to blow.

There is nothing to posting a link here. Just type or copy and paste it in. For instance, https://www.askmehelpdesk.com/plumbing/ takes you to the plumbing forum.

Yes different people use different terms for things. When I was managing a factory, I wasted a lot of time translating what the maintenance people asked for to something purchasing could order. Later I was able to bypass purchasing on little stuff. When the electrician asked for a 2'' Greenfield, I was able to call the supply house counter, and they knew what it was, $20.

I agree the surge fixture would take up expansion, but question how much. I haven't done any calculation, but I would be afraid they would be too small.

According to the AMHD code, you are free to post whatever you want. Everybody else is free to post factual disagreements. Sometimes the AWJ here has to suspend people's license.

Not sure what growler's problem is. Maybe he spilled coffee on his lap and is a bad mood.

I'm not a coffee drinker, Ken.


From what you said in your original post my advice is accurate and correct.

How do you figure that, Ken?


I have been a trouble shooter in a large municipality for 27 years and have come across this problem many times.


And that somehow makes you immune to the occasional mistaken diagnosis?

Counting my four year apprenticeship, I've been Plumbing for for 26 years, yet I still from time to time make some mistakes and errors of my own -- I'm not too proud of that fact, but it happens.


The trouble with plumbing terminology is that different terms have different meaning all over the country.

This isn't an issue of terminology, it's an issue of diagnosis.


I would rather use a generic term that you can use at a plumbing supply store.

And yours was about on par with 'dealie, thingie, thingamabob and thingamajig'.

But really, that's beside the point.


I don't know how to post a link but if you Google water hammer you can see what a water hammer arrester looks like.

I know what "water hammer" is -- I also know that "water hammer" is a symptom or condition and that the solution to this symptom or condition is called a 'shock arrester'.


This will cure the problem if water expansion is causing your pressure relief valve to blow.

No, it most certainly will not.

"Water hammer" and "thermal expansion" are two very different problems created by two very different situations.

"Water Hammer" is caused by the very abrupt closure of the flow of water in a water piping system -- Usually the sudden closure of a single handled valve or the snapping shut of the solenoid of a solenoid actuated fixture or appliance (ice makers, clothes washers and dishwashers being the big three but humidifiers, CO2 pumps and heat pumps are also guilty culprits.)

"Thermal Expansion" is the result of the expansion of heated or super heated (immediate) water in a water piping system.

Just as the two are very different in how they occur, so is the difference in the 'cure'.

I wish you had access to the same 'teaching aids' I do -- In our classroom is a 1" shock arrestor and a 3 gallon expansion tank, both cut down the middle to show how each one operates.

Look me up if you're ever in the area and I'll give you a tour of the teaching aids at my disposal -- When was the first time, let alone the last time, you got to see a 4'x4' functioning bathroom group done completely to scale in lucite?

Ken297, could you explain how a water hammer arrestor with about 2 cubic inches of air can absorb thermal expansion?

This is the first time I have used this Web Site. Thanks to everyone who has provided information... I'm trying to absorb all of it. I replaced the pressure relief valve last night and it is not leaking anymore. The system pressure, measured at the water heater, is still averaging 50psi, with a high of about 60/62 and a low of 40psi (when water is being used). The water heater is a new, high efficiency Bradford White 48 gal, with a power vent system. There is an expansion tank, it does have dielectric fittings, I, guessing there is a backflow preventer built in, but I have nt confirmed that. I do not think that there is a restriction in the system, other than the line losses of a complicated plumbing system consisting of 1/2" plastic. (Plastic lines with crimped fittings/joints). My plan at this point is to buy a pressure gauge, attach it to an outside faucet and check the pressure, and then adjust it to around 70psi. One thing for sure, the overall system in the house has been pressure tested, having run in excess of 100psi for 9 months or so. Thanks again for you help. If anyone thinks that I am on the wrong path please provide your suggestions. I will be out of town for the next 2 weeks, so my lack of response is not disinterest.