Pressure Relief Valve leaking??

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  #1  
Old 10-14-18, 04:15 PM
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Pressure Relief Valve leaking??

I have a natural gas hot water heating system. Getting it ready for winter so I fired it up yesterday. This morning I noticed some water on the ground under the pressure relief valve. This afternoon I upped the thermostat to get it running and I see water dripping out of the Pressure Relief Valve. It's a steady drip not a burst of water.

I did not see when the water starts to leak but it is leaking when the pressure is at 24-25 psi and a temp of around 170. I have two pressure gauges, the original in the boiler and one attached to the drain valve to test. Both read the same number or within 1 psi so I can assume they are correct.

I set the pressure to around 14 psi when cold. Seems to be a good number to get to the 2nd floor radiator. 12 psi is a little low for my house for some reason.

I have a Extol 60 bladder expansion tank. Its about 4 years old. I have a shut off valve going to the expansion tank but no drain valve. In taking off water was shooting all over so there was pressure in the tank. I decided to remove all the air form the tank before removing it from the system to prevent water from shooting out. I took the tank to the sink and emptied it completely. Laid it on the floor and inflated it up to 14 psi. I waited 20 mins, rechecked to make sure it wasn't losing air, and it was still at 14 psi. Don't know if that confirms the expansion tank is good.


After that hooked everything back up, started up the system and it still is dripping water. Can I assume its the Pressure Relief Valve is starting to go? Its factory set for 30 psi and I haven't adjusted it, not sure I can adjust it like the Pressure Reducing Valve. Should my boiler system even be getting up to 25 psi?
Could there still be something wrong with the expansion tank that I missed?

Any advice would be appreciated? Can I test the Pressure Relief Valve somehow?


*edit
Just checked, right now the system has been off for 45 mins. The pressure is 22 psi ,the temp is 160 , and there is no dripping. Also the expansion tank is only hot at the top 1/5 of the tank, everything below that is cool to the touch.
 

Last edited by jasesun23; 10-14-18 at 04:34 PM. Reason: more info
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Old 10-14-18, 06:07 PM
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I had a similar problem. Have you checked the pressure while running? I found if I set the pressure when the circulator is not running the pressure will rise when its running. I would start at a lower pressure and when the boiler and circulator are running slowly add water to desired pressure. hope that helps
 
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Old 10-14-18, 06:18 PM
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Please check the "sticky" at the top of this forum: https://www.doityourself.com/forum/b...sion-tank.html
 
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Old 10-15-18, 04:56 AM
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The 30 Psi. setting of the pressure relief valve is not an exact number for it's setting; it could relieve a pound or 2 above or below that setting. However, relief valves being the last line of defense on a pressure vessel they should be replaced at a regulator interval, say every 5 years or less. Since yours is leaking at 24-25 psi, yours should be replaced now and "NO" they are not adjustable for safety reasons. The fact that your system pressure rises to 24-25 psi when it is heating the water indicates that that tank is too small for your heating system. the next larger size or even 2 sizes larger is recommended. When the boiler fires the pressure will rise but should not rise that much. The cold setting for the system pressure should be the minimum pressure required to have water be expelled from a vent valve at the highest radiator in the system, then add 2-3 psi to that setting. If water is expelled at say 13 psi from that vent I would set the cold fill at 13+ 3 = 16 psi or an abritrary setting of 15 psi minimum.
 
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Old 10-15-18, 06:35 AM
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Many pressure relief valves have replaceable washer. The valves often leak because of debris on the seats that can be cleaned off. Both are easy to check.
 
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Old 10-15-18, 06:43 AM
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Steamboy at 12 psi water comes out of all radiators on the second floor. So I set the cold psi to 14.

I've used multiple manufactures websites to size the expansion tank. The net output of my boiler is 108,000 btu with cast iron radiators. According to that a 60 is the correct expansion tank. Also about 8 years ago I had to drain the system to fix something. I measure around 50 gallons in the system. If going by gallons a 60 is also the correct sized expansion tank.

This is a 65 year old cast iron boiler, I'm not positive but as far as I can remember it always went into the low to mid 20's when it was hot. The temp of the boiler usually gets around 170-180 degrees.

Do you think there is an issue with it jumping 10 psi from cold to running temp
 
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Old 10-15-18, 07:20 AM
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If the pressure rises rises by 10 psi when the boiler fires to it's max temperature of say 180 degrees, that is OK. Your system rises to that temperature and you said that the relief valve leaks. A correctly working relief valve will not leak at 24-25 psi. Also, you can not replace the washer of a leaking relief valve or for that matter rebuild a valve that is used on a heating boiler or pressure vessel, unless you are "certified" with the right license and knowledge/training to do so. And for a residential relief valve it is not cost effective to do so. If this were my system, and I ever had to replace the expansion tank I would install the next larger size. my 2 cents
 
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Old 10-15-18, 01:59 PM
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Expansion tanks are sized not only by boiler BTU's but also by water volume in system and temps.

First off any cast iron radiation calls for a minimum #60. With an older system and a boiler with a large water content like yours where your pressure is increasing by 10 PSI from cold to hot which I think is excessive I would suspect your tank is not large enough to hold the expanded water.

A #60 has a 7.6 gal. capacity and a #90 has a 14 gal. capacity.

Personally, if a system's expansion tank is sized properly there should be no more than a couple of pounds difference between hot and cold temps. 10 lbs. is way to much in my opinion.

Never try to rebuild a relief valve. This is your lifeline and final safety to keep your boiler from blowing up if it's faulty. For the price and safety of yourself and your system buy a new one. 40 years in the business I've never heard of anybody rebuilding a relief valve. I don't know of anybody that even sells the parts or that there were any replacement parts.

If yours is going off at 25 PSI and you know your tank is good and your cold pressure is holding steady and not climbing from a defective feed valve then I would say you have a defective or weak relief valve. You can try to manually open and flush it to remove possible crud stuck in there causing it not to close fully but short of that just replace it, increase your tank size to #90 and you should be good to go.

Just a thought, Hope this helps a little.
 
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Old 10-15-18, 03:13 PM
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I think there may be two problems here. First, the relief valve should be replaced on general principles. They are inexpensive, but you will have to cool down and depressurize your system and drain down below the relief valve elevation.

From your description, it seems that you verified that the expansion tank is properly inflated on the air side. Thus, I conclude that your expansion tank is too small. I would double the size - there is no problem if the tank winds up being oversized. I would prefer to see the present tank replaced with a larger one, but you could install a second tank piped in parallel with your present tank. The tank and the relief valve can both be replaced together while your system is depressurized. You may have a valve between the present expansion tank and the system - which can be temporarily shut for maintenance without depressurizing your system. But don't even think about installing a valve between the system and the relief valve - that is strictly forbidden.
 
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