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-   -   Boiler pressure valve leaks water on shutdown (http://www.diychatroom.com/f17/boiler-pressure-valve-leaks-water-shutdown-159974/)

erockaway 10-13-2012 10:30 PM

Boiler pressure valve leaks water on shutdown
 
Greetings Everyone,

I recently bought a home build circa 76. The boiler was replaced 8 years ago. There is quite a bit of rust on the piping as well. That aside, when we looked at the home, there was a small wet spot near the boiler. No one really knew where it came from. The inspector thought it could have been a spot of oil from the last service.

I saw it come back after running the boiler, but was never sure where it came from. There seems to be a small amount of oil mixed in the water as well. I have run down when other boiler is running to see this first hand, but saw nothing. Later I would go down and see the water again. This lead me to assume it happens AFTER the boiler has run. So I went down after I heard it stop one day and saw water coming from the relif valve. What could cause this to happen after shut down? And why would there be oil mixed in it?

Thank you much in advance.

erockaway 10-13-2012 10:33 PM

Quote:

Originally Posted by erockaway
Greetings Everyone,

I recently bought a home build circa 76. The boiler was replaced 8 years ago. There is quite a bit of rust on the piping as well. That aside, when we looked at the home, there was a small wet spot near the boiler. No one really knew where it came from. The inspector thought it could have been a spot of oil from the last service.

I saw it come back after running the boiler, but was never sure where it came from. There seems to be a small amount of oil mixed in the water as well. I have run down when other boiler is running to see this first hand, but saw nothing. Later I would go down and see the water again. This lead me to assume it happens AFTER the boiler has run. So I went down after I heard it stop one day and saw water coming from the relif valve. What could cause this to happen after shut down? And why would there be oil mixed in it?

Thank you much in advance.

Oh.... I must add that this valve is brand new. .

techpappy 10-13-2012 10:51 PM

1. It seems to me that the latent heat in the boiler builds pressure within near end of cycle after zone valves have shut off...the cushion tank should absorb the expansion from this heat so, it is either flooded..or under pressured depending on type of cushion tank OR the tank is located in the piping system and may get isolated from the boiler when zone valves shut off causing boiler pressure to creep above relief valve set point

what is operating pressure and what is pressure relief valve set at

2. some oil may get into the water due to leaking pump seals if they are the oiled type...cant think of other source for oil ..is the house 1876 OR 1976

erockaway 10-13-2012 10:57 PM

1 Attachment(s)
When I saw it leaking, it looked to be at about 30 which is under the 40 rates psi.

And it's 1976 (though the expansion tank has a 1975 tag on it)

EDIT I just looked. It's a 30psi valve. Would explain the minor release.

I also just kicked on the heat. It's running at bout 14psi


Attachment 58793

The hose is directing the water outside now.

techpappy 10-13-2012 11:18 PM

keep an eye on te pressure..if it rises quickly back up to 30 then your cushion tank is not working...watyer will not compress..just increases in pressure that is why a cushion tank is installed to absorb the expansion from the water heating up..without that the relief valve releases the pressure , then the system cools off and the pressure goes back to 14 which is likely the feed water regulator set pressure..so there should be a schroeder valve ..like on a bicycle tire...on the cushion tank..Shut off feedwater valve and drain boiler until pressure drops to zero..then check pressure on tank..should be at least 15 psig...depress valve stem ..if water comes out then the bladder in the tank is torn internally therefore replace tank..to resume normal operation...if there is no air fill valve then close isolation valves on tank ..shut them and drain tank completely to allow air to fill tank..then close drain valve and open valves to system..if no isolation valves you have to drain system and tank completely to allow the tank to let air into it..check fittings around tank for tightness to prevent air from leaking out.

erockaway 10-13-2012 11:43 PM

3 Attachment(s)
Thank you. When you say cushion, do you mean the overhead expansion tank.


Attachment 58794

The only gauge I see is the on shown in my previous picture

And here is where I would believe I can pump in air. But how much?


Attachment 58796

Some further info


Attachment 58799

how 10-14-2012 02:14 AM

This type of expansion tank in your ceiling belonged to your old system and has no bladder. Turn off the gate valve on the supply to it. Open up the tank's drain valve and drain it. Close the drain valve and re open the supply valve to the tank.
Cycle the boiler again and report back on the pressure after it cycles.

beenthere 10-14-2012 05:01 AM

Make sure you drain the entire tank. In order to do so, when it stops draining initially, you need to allow air to get into it to continue to drain.

biggles 10-14-2012 07:52 AM

tank is probably full so the relief is doing its job,as suggested drain it down open the riser let it flush out then shut the riser and drain line let the system water pressurize it.draining of that tank on strat ups in the fall nd mid winter is a good habit to keep that shutdown(stat satisfied) pressure between 20-30PSI..are you running old radiators or baseboardon the rooms...air vent on that tee might be adding to the "leakage burp" :wink:

hvactech126 10-14-2012 10:20 AM

Quote:

When I saw it leaking, it looked to be at about 30 which is under the 40 rates psi.
40 psi relief valves are not allowed on residential systems. Also the relief piping must be done in solid pipe and piped to within 6" of the floor.

techpappy 10-14-2012 10:30 AM

the vent on top of the boiler where you thought you could put air in is actually an automatic air vent to vent any air off the top of the boiler..it should not be installed at that location as it can actually allow air to enter into the system..recommend you remove and replace with manual shut off cock that can be used to manually check/vent any air ..should have manual air vents on each radiator with only one automatic air vent on highest possible location in system or none at all

The exsting cushion tank could have slow leaking fittings or a pin hole leak in tank allowing escape of the air cushion.
If you find that cushion tank is "flooding" i.e., is leaking air out and will not hold the "cushion" then you could replace it with a bladder type tank that can be installed on the floor and connected into pipe that goes to existing cushion tank...that way it would not matter if the tank floods..you could also shut off any valves to it and leave it out of service but, only if new XTank is installed.

erockaway 10-14-2012 11:31 AM

The above tank doesn't appear to be full. I can rock it which is petty easy and here the water swishing around. I will try later to drain it and see if that helps.

I did look up new cushion yanks and may go that route. I'm also in the process of getting quotes for a gas conversion. Trying to determine if keeping this one and converting it is the best route. Or replacing it altogether. There is about a $5,000 difference

techpappy 10-14-2012 12:17 PM

are all the valves between boiler and tank open? good to make sure because you definitely do not have enough cjushion

furthermore ..if the over pressure problem haas been chronic for several years then chances are that the boiler is full of sludge ..this is due to all the impurities, in the make up water being precipitated out in the boiler..if so, it this prevents proper heat exchange (very low efficiency) high stack temperatures $$$$up the chimney and liklihood of causing leaks in boiler due to overheating of fireside surfaces also due to lack of circulation in the boiler because of the sludge..if you have a drain valve at bottom of boiler you can open it for about 15 seconds ata time when it is at operating pressure..this will help to blow out any sludge in bottom of boiler however it would be best to remove connecting piping wherever possible to flush out with hose/pressure washer...not required if you remove bottom drain and observe there is no sludge, i.e., waterside surfaces squeaky clean....hopefully you caught the problem at initial stages and won't be an issue.

REP 10-15-2012 06:30 AM

The air vent located next to your pressure relief valve is in a spot where it does nothing.It needs to be in the flow of water in your system so that any air bubbles in water have a chance to go into that vent and then out of the system.Where it is now,it sees no water movement.
Your expansion tank should be a third to a half full.Do not shut off the valve going to the expansion tank.If you do the water in the system has no place to expand.The "oil " you mentioned is probably something that was put into system to control minerial build up or to possibly lubercate the water going through zone valves.I used to use it for white rogers zone valves because it was metal to metal at the moving parts.

techpappy 10-15-2012 08:50 AM

sometimes an air bubble can occur at top of boiler causing an air lock and prevent circulation of heating water..that is why the auto air vent was installed there. However as I said previously should only be a manual air vent for that purpose as it can in fact allow air in at that point

We recently assisted another OP who could not get heating water circulation due to air lock at top of boiler. Once he cleared that everything OK.


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