I Replaced Pressure Relief Valve on Rinnai water heater (twice!!). New one does not hold ANY pressure

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While I can't provide a definitive answer, since I'm not the manufacturer, nor do I, or have I ever worked for the manufacturer. I can try to provide a logical, fact based answer that may be close to the truth.

When water is heated, the pressure in a closed system increases. If the pressure increases beyond the tripping point of the T&P valve on the heater, the valve should open to release some of the pressure. This release usually involves very hot water and steam, released in a controlled manner. If you install a pressure relief valve set lower than the T&P trip value, The relief valve will open long before the T&P valve possibly releasing hot water and steam in an uncontrolled way. This could lead to injury to occupants, or damage to property.

It's possible that your area has not adopted the use of backflow prevention, so this extra pressure can simply be released back through the distribution system. In which case, you'll probably never see either relief valve...

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Will revise answer once more information about the unit is given. This answer is assuming that the issue is low water pressure, as opposed to low gas pressure. IF the issue is indeed low gas pressure, i can edit my answer to accommodate the probable causes for this issue as well.

These are the possible causes for the issue from most common to least (1 and 2 are by far the most common causes for this issue):

Calcium build up of the heat exchanger (causing a restriction, will need to be flushed) Blocked or dirty inlet filter Faulty flow sensor (made of plastic, commonly will break or crack in older style Rinnai units) Under sized inlet or outlet lines to and from the unit Faulty control board/Short in the wiring harness somewhere Plumbing issues within the structure (or inlet feed taken from improper location) Issues with water pressure supplied by the city

If you have never had the unit serviced, i would highly recommend it. Flushing the unit with vinegar and...

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The first thing you'll want to do, is to insure you're rotating the proper direction. Make sure you're rotating the valve in an anticlockwise direction.

Apply a liberal amount of penetrating oil; allowing it to soak in for a bit, then give it another try. This will help clean the threads, as well as providing a bit of lubrication. Giving the threads a good second blast of penetrating oil can often remove more dirt and corrosion, which can be just what's needed to get the valve turning.

Using a wrench with a longer handle; or a breaker bar, can often help loosen stuck valves. Just be careful, you may be able to exert enough force to actually snap the valve.

Tapping the end of the wrench with a non-marring mallet, can also help loosen a stuck threaded joint. Again, too much force can cause collateral damage, so be careful. Place the wrench on the valve, and gently rap the end in the direction of rotation.

Note:
Make sure you have the...

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Pressure relief valves sometime develop a drip when opened for the first time in years. Try opening and closing it a few times to see if it will seat itself. If you have a large leak or the drip doesn’t stop on its own in a day or two, the valve will need to be replaced. Whether you can replace it yourself will depend on your skill level, but as far as plumbing repairs go, it’s not that difficult.

If you do try to fix it, here are the basic steps involved by Orange Restoration San Diego:

1. First, turn off the gas to the water heater, or flip the breaker if it’s electric.

2. Close the cold water cut-off valve going into the water heater.

3. Open the valve at the bottom and the pressure relief valve for a minute to drain a little water out of the tank and relieve the pressure.

4. Remove the overflow pipe from the pressure relief valve. If it’s been glued or soldered in place, it may have to be cut off.

5. Use a pipe wrench to unscrew the old...

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How To Diagnose And Replace A Faulty Pressure Relief Valve In A Hot Water Heating System, is an article that homeowners will be happy to find. Saving hundreds of dollars and performing this repair yourself is a very tempting opportunity. Learning what the functions of the pressure relief valve are is a necessity before you start to work on one.

What Does A Pressure Relief Do?

Pressure relief valves are installed in boilers and water heaters. They are specifically designed to go off and relieve any extensive pressure that can build up in this type of equipment for a variety of reasons.

Hot water heating systems will use a 30 pound per square inch pressure relief valve to obtain the safety level they wish to maintain within the system. This means that a hot water heating system pressure relief valve will go off and release water when the pressure exceeds 30 pounds.

Hot water heaters employ a 100 pound per square inch pressure relief valve and this valve...

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Replacing the T&P valve is not a difficult task but we do want to make sure we are safe. I personally suggest you drain off the tank completely before performing this task. Not only will this help to eliminate possible messes and accidents, it should be done yearly and it's likely you are due to perform this maintenance.

Now that the tank is drained, open the valve all the way to make sure all pressure is released from the tank and proceed to disconnect the discharge line. It's possible that you are lucky enough to have a valve on the side of your tank or be able to unscrew this line in it's entirety because you have the ceiling height to do so. However, many of us will have our valve on top and not have the ceiling height to allow this. The tube will hit the ceiling if we try to unscrew it in one piece so we will have to cut it with our tubing cutter or hacksaw. Be sure to put on wrench on the discharge and one wrench or pliers on the valve to apply opposing pressure. This...

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well most Pressure Relief Valves (PRV's) leak because of bad seals from junk in your water that eats the rubber seal but sometimes it can be to much pressure or the water heater is too hot. I would check to make sure your pressure or temp is not the cause before I would replace the PRV. Almost all potable water heater PRV's are set to release pressure at 150 PSI. If its leaking because of the bad seal then you have to replace it because most are non replaceable parts.

A T&P valves is unique in that is can relieve either pressure (150 PSI) or temperature (210 F) a "Relief valve is used for liquids and a safety valve is used for vapor such as air or steam.

A PRV is a pressure reducing valve and normally found on either the supply to a Hydronics boiler or incoming domestic water and if one is failing you would also get telltale signs such as water hammering (hydraulic shock)

If the T&P valve seeps this could caused by water expanding when heated called...

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Water heater leaks can occur for a variety of reasons. It may be something as simple as a slightly open drain valve to a severe issue such as a corroded hot water tank. Most of the time, it’s due to faulty plumbing connections or valves that have failed. At the very least, a leaking hot water heater is an annoyance. If not properly addressed, this small nuisance can quickly turn into a major problem. While a small amount of water may seem harmless, it may eventually cause substantial water damage to walls, floors, and subfloors if the leak is not taken care of. In the most severe cases, the area around the water heater could even experience flooding. What could have been a quick, inexpensive fix has now turned into costly repair bills.

In addition to water damage, serious health issues can arise due to mold and mildew growth in those wet and damp areas. According to the CDC, children or those with severe allergic reactions or immune suppression are at highest risk of...

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How to install, check and replace temperature and pressure relief valve - TPR

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Water heater relief valve or TPR valve is a safety device that is temperature and pressure sensitive and designed to limit its levels in the tank type heaters. Pressure relief valve is also required on tankless water heaters per ANSI and CSA standards.

When water in the tank heater is heated, temperature is rising. Once the temperature is reached, the unit, thanks to the thermostat and control valve, automatically shuts down. If, for any reason thermostat or control regulator quits working properly and fails to stop the heating, temperature, pressure and volume will reach the dangerous values.

The dangerous level is when the water is heated beyond its boiling point of 212 F. The overheated water is turning into steam instantly, increases its volume and releases the amount of energy enough to become a steam-powered bomb. This is why...

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I just finished replacing the pressure relief valve on my Rinnai hot water heater. Everything went well, I turned on the cold input and wham, water just started gushing out of the relief valve. All the specs line up on the valves (150 PSI), in fact the new one has a higher BTU/HR rating by a long shot (500,000 old vs 934,000 new).

I have to ask now. Could I have done something wrong during installation? It was all so obvious what to do, teflon tape, screw the valve into the hole, put the drain pipe on the bottom and done.

After inspection of the new valve it appears that the inner gasket had come unseated therefore not letting the valve close. I assumed it was defective, so I exchanged it for a new one, the gasket looked good.

The replacement had a seated gasket, I opened and closed it manually and it seated nicely. I installed, same as before, as soon as I put some water pressure to it, it just started gushing and wouldn't closed. When I removed the 2nd new...

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A water heater leaking from the bottom is not always an indication of tank failure. Before you resign yourself to replacing the entire water heater, take a few minutes to determine where the leak is actually coming from, and you may be able to fix the leak yourself with little or no cost. Before you being working on the water heater, turn off the power and gas to the heater to avoid possible shock or burns.

See also: Water heater leaking from the TOP

Identify the Leak

The first places to check if it appears that you have a hot water heater leak from the bottom are the drain valve and temperature & pressure relief valve (T&P valve). The leak may even be at the top of the water heater and simply running down through the body of the heater before escaping at a lower level. Look for any visible signs of a leak on the top of the water heater and all pipes leading to or away from the heater. You can also remove the access panels and check for moisture in the...

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The pressure relief valve on a hot water heater can leak over time.

I just flushed my hot water heater as you mentioned and now the pressure relief valve is leaking. Is this something I can replace on my own, or should I call a plumber? -Leighton

Hi Leighton,

Pressure relief valves sometime develop a drip when opened for the first time in years. Try opening and closing it a few times to see if it will seat itself. If you have a large leak or the drip doesn’t stop on its own in a day or two, the valve will need to be replaced. Whether you can replace it yourself will depend on your skill level, but as far as plumbing repairs go, it’s not that difficult. If you do try to fix it, here are the basic steps involved:

First, turn off the gas to the water heater, or flip the breaker if it’s electric. Close the cold water cut-off valve going into the water heater. Open the valve at the bottom and the pressure relief valve for a minute to drain a little water out...
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By Reuben Saltzman In Expansion Tanks, leaking relief valve On January 22, 2012

When a temperature and pressure (T&P) relief valve at a water heater leaks, it’s usually a simple fix; just replace the valve. These valves cost less than $15, and replacing the valve is a very basic job – just drain some water out of the water heater, remove the discharge tube, and replace the valve. No big deal.

Unless it starts leaking again.

If a recently replaced T&P relief valve starts leaking again, it probably means that the relief valve is only doing it’s job; it relieving excess pressure in the water heater. When this happens, the fix gets a little bit more involved. I’ll explain.

When a water heater heats up the water in the tank, the water expands. When this happens, the water typically ends up expanding back out the cold water inlet, all the way back to the water supply coming in to the house. The municipal water supply for the house acts as a gigantic expansion...

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