tankless on boiler popping relief

tim_20

my dispatcher has a tankless coil that keeps dripping or discharging the relief valve usually wneh the burner shuts off. going by in am to look at i know there is no flow control valve on it and it is rated a 3gpm he also states relief is a 150 lb relief any ideas? i know one of our other guys replaced last year. could water hammer be a cause??  thanks tim

Coany

water hammer could be the cause

did they just get a new fridge or washing machine or dishwasher?



 did they recently change the water meter to the type with a check valve?



I've found quite a few who got new water meters last summer with this problem

STEVE PAUL_3

POPPING relief valve

Call in a QUALIFIED professional to remedy this.

The 150psi relief valve is NOT the correct valve!

 If the boiler is a steam boiler, install la properly rated 15psi relief valve. If the boiler is a hot water boiler install a 30psi relief valve. The 150psi valve is a water heater relief valve and is being used in an improper application. YOUR SITUATION IS VERY DANGEROUS.

The next thing to do is to check the tank less coil for leaks. You are not the guy for this job. If you were you would have known about the wrong relief valve installation.  

Mark Eatherton

Uhm, Steve....

Not sure if you're reading it the same way I am, but it appears that his problem is on the potable side of the coil, not the boiler side. It also sounds like possibly he works for a service company.In any case, I'd suggest that he put a recording pressure device on the potable hot water and see if it is temperature or pressure that is activating the valve, and yes, it cold be water hammer that is causing the valve to SPIT on occasion.If it is kinetic energy, either address it with the use of a water hammer eliminator or choke the flow to the offending device to slow down the water and consequent hammer.It COULD also be related to the expansion of water being heated, which can be addressed with a potable water expansion tank on the cold inlet to the coil.If it is not pressure, then it is temperature.ME

Ron Jr._3

I agree with Mark

More than likely the relief valve is working as it should - relieving the excessive pressure . It'll happen often if noone uses a sink for a long period and there's a big temperature swing in the boiler . A potable expansion tank is a good idea on every domestic water supply regardless . We still install coiled boilers probably 75% of the time ( very unique area here ) , and see this happen alot .  

Kevin_in_Denver_2

Expansion device required by code but not often found

I've been having some water heater issues also, ever since my backflow preventers were installed

by LAW.   Apparently ignorant plumbers and inspectors signed off on BFPs without an expansion device.

I didn't have weeping T&P relief valves, I just had premature water heater tank failure.



From the Watts website (sorry the nice diagrams didn't copy over):



[url=http://www.watts.com/pro/divisions/watersafety_flowcontrol/learnabout/learnabout_thermexpansion.asp#generalinfo_plumbingcode]http://www.watts.com/pro/divisions/watersafety_flowcontrol/learnabout/learnabout_thermexpansion.asp#generalinfo_plumbingcode



 

Plumbing Code Requirements



Thermal Expansion Control



Plumbing codes require that thermal expansion control be addressed in plumbing systems. A temperature and pressure relief valve is not considered a thermal expansion device.

This is because when water is allowed to continuously drip from the

T&P relief valve, minerals from the water can build up on the

valve, eventually blocking it. This blockage can render the T&P

valve useless and potentially lead to hot water heater explosions. The

International Plumbing Code (IPC), Uniform Plumbing Code (UPC) and

Standard Plumbing Code all require thermal expansion control to be

addressed.





Expansion Tank Construction





Section VIII of the ASME Boiler and Pressure Vessel Code states certain

requirements that must be met by an expansion tank for it to meet ASME

construction specifications. The Watts Series ETA, ET-RA and DETA tanks

all meet these ASME requirements.



Water Containment vs Water Relief Solutions



Water Containment solutions allow for thermal expansion while

containing thermally expanded water in the plumbing system. The Watts

full line of thermal expansion tanks are considered water containment

devices. These products require no installation of discharge lines or

drains.



Water Relief solutions discharge thermally expanded water at a pressure

setting that is below the setting of the water heater’s temperature and

pressure relief valve. Watts offers a variety of water relief solutions

that can be installed on the system piping, in a water closet or on an

outside faucet. These products must be piped to a suitable drain or

discharge location.

 

Expansion Tanks -

How a Diaphragm Expansion Tank Works



  When water is heated in a closed system it expands. Water is not

compressible, therefore, the additional water volume created has to go

someplace. When an expansion tank is installed the excess water enters

the pre-pressurized tank (figure 1). As the temperature and pressure

reaches its maximum, the diaphragm flexes against an air cushion (air

is compressible) to allow for increased water expansion (figure 2).

When the system is opened again or the water cools, the water leaves

the tank and returns to the system.



figure 1. As the water temperature increases, the expanded water is received by the tank.

 

figure 2.

As the water and pressure reaches its maximum, the diaphragm flexes

against the air cushion (air is compressible) to allow for increased

water expansion.

 

Kevin_in_Denver_2

Should be installed rightside up

Ron Jr.,



Your photo shows the the expansion tank installed upside down.  There's a couple of reasons that's not recommended with diaphragm tanks, whether it's on the potable side or the closed side of the boiler.



The reasons are fairly minor, but now I will go look them up.

TonyS

What is the incoming water pressure

and is there a pressure regulator on the incoming potable. Have seen many of these cheap regulators weep through over  night . Leave a test gauge with a manual reset arm on overnight.  You should install that style mixing valve with a 12-18 inch thermal trap.

Ron Jr._3

Tony

We used to install them with the trap . But our service guys tell me they're changing the inserts just as often when they have a trap and when they don't . Which is very rarely .



Kevin , we install the expansion tanks like that for a few reasons . One being the feedback from our service guys again .......... it makes no difference where the tank is located , they fail in every position . Another is the theory that any crap in the system will fall down into the tank , possibly lodging between the diaphragm and tank itself causing a leak . Last is safety ........ I saw a waterlogged tank crush a guys fingers when it was hanging down close to the top of a boiler .   

Big Ed_4

Pressure Test

Install a pressure gauge with a dead needle.... If its a pressure problem the needle will rest at 150# . May be a spike or check valve on the system .. Pressure reducing valve will take care of a spike.You Would need to to add a thermal expansion tank with it too .. A steady increase on temperature rise will indicate a check on the system .. Temperature could be a factor too as you know....

Kevin_in_Denver_2

Upside down diaphragm tanks

One reason not to install them upside down on the closed (boiler) system is that they could fill with air (O2, N2, CO2). One idea behind a closed system is to get rid of corrosion causing O2 as quickly as possible, so you're not really accomplishing that. As I said it's a minor reason since it's not a lot of O2, therefore not a lot of corrosion.



On the other hand, an upside down tank will perform its expansion tank duties for a long time after the diaphragm fails. At that point it works just like an old style non-diaphragm tank. It will eventually rust through, however.



A potable water expansion tank can be installed in any orientation because that water is chock full of O2 and no one is trying to get rid of it.

toilburn

toilburn

SOMETIMES THE CITY WATER PRESSURE IS INCREASED DUE TO NEW PIPES OR NEW STORAGE TANKS AND NOW IT IS ALMOST UP TO THE 150PSI