Who's correct: The town or the plumber? Expansion tank for water heater.

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Heidi Homeowner

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What causes a PRV to be overridden?

How do I avoid a home flood?

I edited my post. I'm no longer interested in who's correct. I got caught up in a he-said, he-said and it was too much to follow what everyone else was saying about what the other party was saying.

I just want to understand how to avoid a home flood if a PRV is overridden by dirt or pressure from a fire hydrant or work being done in town, etc. Is having an extension tank good enough?

Thank you in advance.
 
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Dana

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1) PRV stands for Pressure Reducing Valve, which reduces the pressure being fed to you your house to something lower than the water main pressure. The thing on the water heater is a T & P ( Temperature & Pressure) relief valve codes require one on every hot water heater to keep the water heater from exploding.

2) Neither are correct. A PRV is not a pressure regulator, it can only reduce pressure in only one direction- from the water mains (higher pressure side) to your house (low pressure side). You could boil the water in your plumbing and hit 1000 PSI (if something didn't break or open up first, such as the T & P valve, which got stuck), and the PRV would not send that pressure back into the mains. So it can't reduce pressure from heating volumes of hot water in your system. The system absolutely needs an expansion tank to be installed whenever there is a PRV or check valve preventing water flow back into the mains. The water in the tank was cold when the water heater was filled, but expands to a higher volume when it's heated. This is normal. If the plumber knew that there was a PRV on the street he/she should have still installed the expansion tank- it's simply not optional. It was an error on the plumber's part not to make you aware of this exact consequence when you "...opted out of the expansion tank ...".

The notion that your plumber used a fire hydrant to pressurize your house is simply ridiculous on the face of it.

3) There are systems that will shut off the water feed to the house based on water depth in the basement, if you really want to go there.
 

Smooky

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A PRV usually stands for a pressure reducing valve as Dana mentions above. Sometimes people get confused and refer to a pressure relief valve as a PRV. It sounds like that s what you are talking about to me.
Pressure relief Valve
When cold water heats up it expands and a pressure relief valve lets a little water out each time it expands. They should not be installed in a location that cannot get wet unless piped to a drain etc. They use to be used a lot as an alternative to installing a thermal expansion tank. The price now isn't that much different so most people use the tanks. There is no water released with a tank. With a pressure relief valve customers often think something is wrong when it is working as it should.
 

Jadnashua

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Where I live, whether your water system is open or closed, to pass an inspection, you are required to have an expansion tank AND a vacuum relief valve when installing a water heater. In other locales, you may only need an ET when you have a closed system. IMHO, a pressure relief valve only makes sense if you want an emergency backup for your PRV (pressure reduction valve). If the PRV failed, the pressure relief valve my run constantly. If it is plumbed where you don't notice, you could waste a lot of water. Unless your supply water pressure was ridiculously high, a failed PRV might not hurt anything, especially sort-term (unless you have a smoking gun, weak, nearly worn out component somewhere, and a relief valve may not work then, either!). You'd probably notice the significant increase in pressure and fix things.

As was already explained, water expands when it gets heated, and a PRV prevents that expanding water from pushing back into the supply lines to relieve it. Since the copper (or most types) of pipe in the home do not blow up like balloons, any expansion causes the pressure to rise very quickly...it needs somewhere to go, and an ET is the accepted location, not dumped on the ground from a pressure relief valve. NOte, this happens every time you use hot water, then stop...the incoming cold water expands when the WH turns on, and has to go somewhere. The ET really helps to keep things stable without stressing the devices in your home. They don't last forever, but are not particularly expensive, either. Usually a 5-minute task to put in a new one.
 

Heidi Homeowner

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1) PRV stands for Pressure Reducing Valve, which reduces the pressure being fed to you your house to something lower than the water main pressure. The thing on the water heater is a T & P ( Temperature & Pressure) relief valve codes require one on every hot water heater to keep the water heater from exploding.

2) Neither are correct. A PRV is not a pressure regulator, it can only reduce pressure in only one direction- from the water mains (higher pressure side) to your house (low pressure side). You could boil the water in your plumbing and hit 1000 PSI (if something didn't break or open up first, such as the T & P valve, which got stuck), and the PRV would not send that pressure back into the mains. So it can't reduce pressure from heating volumes of hot water in your system. The system absolutely needs an expansion tank to be installed whenever there is a PRV or check valve preventing water flow back into the mains. The water in the tank was cold when the water heater was filled, but expands to a higher volume when it's heated. This is normal. If the plumber knew that there was a PRV on the street he/she should have still installed the expansion tank- it's simply not optional. It was an error on the plumber's part not to make you aware of this exact consequence when you "...opted out of the expansion tank ...".

The notion that your plumber used a fire hydrant to pressurize your house is simply ridiculous on the face of it.

3) There are systems that will shut off the water feed to the house based on water depth in the basement, if you really want to go there.

Thank you for your post, Dana. I think I wasn't clear with what I wrote.

1) Thanks for explaining the difference between the PRV and T & P relief valve.

2) The plumber didn't know there was a PRV in the street. He had suggested a PRV and expansion tank when we purchased the water heater a few years ago, but we opted out because we didn't understand that they were necessary. He has since installed an expansion tank, after our home almost flooded. It wasn't code when we installed it. I see now we should have installed it anyway.

I never said that my plumber used a fire hydrant. I said that someone told me that the reason for the high pressure (over 100 psi's) was that it was possible a contractor was using a fire hydrant illegally, or that dirt got into the street's PRV, or that someone was doing work around town. The plumber actually was horrified at the thought of someone using a fire hydrant.

3) How common is something like that to install? What's the expense? I was really hoping to learn how to prevent this from happening again. I was fortunately home to shut off the water heater when I heard water gushing out of it. Is the expansion tank enough to prevent this from happening? Thanks.
 

Heidi Homeowner

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A PRV usually stands for a pressure reducing valve as Dana mentions above. Sometimes people get confused and refer to a pressure relief valve as a PRV. It sounds like that s what you are talking about to me.
Pressure relief Valve
When cold water heats up it expands and a pressure relief valve lets a little water out each time it expands. They should not be installed in a location that cannot get wet unless piped to a drain etc. They use to be used a lot as an alternative to installing a thermal expansion tank. The price now isn't that much different so most people use the tanks. There is no water released with a tank. With a pressure relief valve customers often think something is wrong when it is working as it should.

Thank you for your reply, Smooky. I didn't understand the difference between a pressure reducing valve and a pressure relief valve.

I was told the valve on the water heater needed to replaced because it was "stuck", or "stuck open", because I'm assuming it kept the water heater from exploding when I heard all the clanking noises and it instead released water and now it needed to be replaced? At first I thought "stuck" meant it didn't do its job and it malfunctioned by the other plumber explained it as "stuck open".
 
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Heidi Homeowner

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Where I live, whether your water system is open or closed, to pass an inspection, you are required to have an expansion tank AND a vacuum relief valve when installing a water heater. In other locales, you may only need an ET when you have a closed system. IMHO, a pressure relief valve only makes sense if you want an emergency backup for your PRV (pressure reduction valve). If the PRV failed, the pressure relief valve my run constantly. If it is plumbed where you don't notice, you could waste a lot of water. Unless your supply water pressure was ridiculously high, a failed PRV might not hurt anything, especially sort-term (unless you have a smoking gun, weak, nearly worn out component somewhere, and a relief valve may not work then, either!). You'd probably notice the significant increase in pressure and fix things.

As was already explained, water expands when it gets heated, and a PRV prevents that expanding water from pushing back into the supply lines to relieve it. Since the copper (or most types) of pipe in the home do not blow up like balloons, any expansion causes the pressure to rise very quickly...it needs somewhere to go, and an ET is the accepted location, not dumped on the ground from a pressure relief valve. NOte, this happens every time you use hot water, then stop...the incoming cold water expands when the WH turns on, and has to go somewhere. The ET really helps to keep things stable without stressing the devices in your home. They don't last forever, but are not particularly expensive, either. Usually a 5-minute task to put in a new one.

Thank you for your post, jadnashua. This is way above my head but thank you for trying to explain it. The plumber read the pressure as 110 psi's shortly after the water heater gushed water out of the pressure pipe, but it went back down to the 60's. When we had the water heater installed it was code yet to have an expansion tank. I was told that is a fairly new code. An inspector is coming out to inspect the new expansion tank and new relief valve for us.

I'm still uncertain as to what actually failed which caused the almost-flood.

What is an ET? That sounds like a smart idea.
 

Dana

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Installing something that automatically shuts off the water to the house isn't very commonly done in the US. Most leaks start as minor flows not catastrophic deluge, and in homes that are occupied they're typically discovered and dealt with before major flood damage is a possibility.

The most common big leaks happen when say, a long ignored dripping leak from a old washing machine gives up the day after you've left for a 2 week vacation. The cheaper solution is to manually turn off the water when you plan on being away for an extended period. Catastrophic deluge from hot water heaters are possible, but rare. In many states the building code requires that the outflow of the T & P valve be plumbed to direct the water drain to prevent both the flood and scalding.

When a PRV valve fails it doesn't usually fail catastrophically- it usually just seeps, and if the lowest pressure leak point is the T & P valve (often is), having the outflow of the valve plumbed to dump into a drain (as required by code in many locations) isn't an outrageous expense. If the seepage rate is low you might not even notice it (safe for the house, but could add up on the water heating bill.)

A basement sump and float activated sump pump is a common feature in many houses, and that too would usually be able to keep up with a fairly major leak.

I would take "ET" to mean Expansion Tank, no?

The expansion tank needs to be pre-charged to your intended system pressure for it to work optimally. Most expansion tanks sold into the hydronic heating market come pre-charged to a much lower pressure than 60psi. If you water pressure measures 60psi (go ahead and measure it), shut off the main water to the house and open a tap (cold or hot) until the pressure is low. Pump up the tank with air until it's 60psi (they usually have the same type of valve as a car tire), then turn on the water to the house. On potable water systems the expansion tank should last for decades, but periodic checking of the pre-charge (say, every couple of years) is prudent. With the water to the house turned on you can't test it, you must bleed down the system pressure first, as described. If gets to the point where it's losing pressure, the valve can be replaced. If the internal bladder fails and leaks you may only discover it when the T & P valve opens up. When you tap the side of the tank on the air-valve end it should ring, and on the plumbing end it will be more of a thud. If it thuds on the air valve end it's either completely lost it's pre-charge, or the bladder is shot.

bladder-operation2.jpg
 
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hj

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Using a fire hydrant for ANY purpose, authorized or not, does NOT "increase" the pressure in the system. If anything it lowers it if several pumper trucks are drawing from the same main. If you depress the pin in the air valve and water comes out, the tank is shot. If NO air comes out it is waterlogged and repressurizing it may restore it to service.
 

Gary Swart

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You asked about how difficult expansion tanks are to install. Really quite simple. They are installed in the incoming water line. The line is cut and a small section taken out and a tee is used to reconnect the pipe ends*. The expansion tank come with an adapter to connect the tank to the tee. That's it for the basic install, but the tank must be supported. There are several ways to do this depending on the location of the tank. The only plumbing skill is knowing how to sweat (solder) copper fittings. It's a pretty easy DIY job. You do have to match the tank's air pressure to the incoming water pressure. Pressure gauges are inexpensive and are available at any hardware store, they are handy to have anyway. Air is applied to the tank just like airing a tire, and the pressure is check with a tire pressure gauge.
*If when the pipe is cut you can move one or both pieces enough to get the tee inserted, no need to cut the small piece out.
 

Jadnashua

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In lieu of buying a water pressure gauge, when the ET is installed with somewhere below the supply pressure (they often come precharged to 40psi which should work), just use a car tire pressure gauge on the fill valve - the air pressure will become the same as the water pressure which is why you must have the water turned off and the pressure relieved in the water supply system to check and verify the ET's air pressure. Once you know the water pressure, turn the water back off, open a faucet to relieve all pressure then pump the tank up to that value. Close the faucet and reopen the water shutoff, and you're done. It's handy to have a water pressure gauge, but not required in this case. By setting the precharge to the same as the water pressure, the air bladder is at its neutral position and will last the longest since it won't have to move as far during cycles or be under as much stress.
 

Master Plumber Mark

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The expansion tank needs to be pre-charged to your intended system pressure for it to work optimally.


The plumber simply made a common mistake and needs to come back out and install one with the pressure set equal or slightly higher than the incomming pressure... I dont know who is gonna foot the bill for this but it cannot be that much money involved ..... just pay the guy to come back out and move on....

I would also suggest that you pipe the t+p drain to the nearest floor drain or sump pit
as an extra precaution
 
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