Occasional relief valve blow-off from Burnham Series 2 205NI-G2

lbeachmike

Last winter a small amount of water was noticed from relief valve discharge. Boiler pressure was found to be high. My plumber removed pressure from the system and it appeared to maintain at the lower pressure levels (11 to 15 pounds.) A bucket was placed by the relief discharge pipe and no further discharge was seen through last winter.

The other day I found the bucket with about six inches of water. I emptied it and have monitored and there is a tiny bit so far.

I have checked the pressure gauge while the boiler is operating and I see 14 to 20 PSI.

What could be gradually increasing the pressure over time? Is it assumed that the relief blowoff is likely due to higher spikes in pressure during longer operating times that I just haven't yet noticed?

When I have my plumber or heating company return, what would be the appropriate troubleshooting steps?

Jamie Hall

Make sure that the expansion tank is still good (only air, no water, but air at the right pressure at the Schrader valve) and check the pressure reducing valve on the makeup water feed. For starters.

lbeachmike

Jamie Hall said:

Make sure that the expansion tank is still good (only air, no water, but air at the right pressure at the Schrader valve) and check the pressure reducing valve on the makeup water feed. For starters.

What is used to test the pressure off the expansion tank? The same PSI gauge I use for my tires?

How is proper operation of the pressure reducing valve tested?

Unfortunately, most any plumbing/heating company I have ever used in my area does not do any actual testing - they just replace components. This is why I am posting here to help with my own knowledge.

Both my heating company and plumber previously said the expansion tank sounded fine from "the tap test" - and my plumbing and heating company both are considered to be among the best around here, getting recommendations from plumbing supply companies and the like.

EdTheHeaterMan

Unfortuniatly, most contractors/plumbers don't have a real grasp of how the expansion tank works and how to test it. And trying to get a DIY homeowner too understand it can be time consuming, BUT it is a very simple concept.
1. When water is heated, it expands
2. On a closed system that water needs a place to go
3. The expansion tank (with or without the diaphragm) has an air cushion. That air cushion will compress when the water expands, giving that water a place to go.
4. If the air in that tank finds its way out of the tank in any way, the amount of space for the water to expand becomes smaller.
5. To compensate for that smaller area, the water pressure will increase
6. Eventually as more air leaves the tank there is not enough air to compress and the tank becomes waterlogged and the pressure increases to the point where the relief valve will discharge the excess pressure.
7. To solve the problem the air must be replaced into the expansion tank.
8. Sometimes that can be easy, other times not so easy.


The way your tank is installed the testing location is hard to get to. But not impossible.
Some professionals believe that just pushing on the test port Schrader valve is a good enough test. It is not. That is like pushing the Schrader valve on a tire to see if it is properly inflated. We both know that only tells you that there is some air pressure in the tire. It does not tell you what the pressure actually is. Same with the Extrol brand tank you have. And that testing procedure will only let air out of the tank, you never want air to leave the tank in any way.


Another fact is that the membrane in the tank that separates the air from the water can allow air to migrate out of the tank into the water on a molecular level, accounting for about 1 PSI of pressure drop per year. So proper testing will increase the life of the tank, if the pressure is lower than it should be, the test will let you know to add pressure to the tank in order to keep the tank operating properly. A bicycle pump is the best method of adding pressure to the tank.


The test must be completed with no water pressure from the boiler connected to the tank. Boiler water pressure added to the air in the tank will give a false reading. Since there is no isolation valve to uncouple the expansion tank from the boiler pressure, you must lower the boiler pressure below the tank pressure to get an accurate measurement.


As you can tell, this can be hard to understand by the DYI and PRO alike.


If you are interested in doing this test yourself, you will need an accurate tire pressure gauge that can measure low pressures. As low as 12 PSI.


I can walk you thru the procedure if you need it.

EdTheHeaterMan

As far as testing the auto fill valve (PRV), that is done once you know that you have the proper pressure in the expansion tank. After you have the system filled with the proper water pressure you check to see if more water is passing thru the PRV. This can be done with a mechanic’s stethoscope to listen for the water flow to stop. Similar to the way a toilet tank fills. Eventually the water flow stops. If it does not, the water in the toilet tank will reach the overflow and the water will continue to trickle into the toilet bowl.


The water will flow thru the PRV to get the boiler pressure to the desired pressure (usually 12 PSI). Once the pressure reaches the set point the water flow will stop. If it does not stop, then you can adjust the pressure setting until the flow does stop. If you can not get the water flow to stop, then the PRV is defective or needs to be cleaned out. Since that valve is connected to potable water, there may be corrosion or debris build up in the valve and cleaning the valve may correct the problem but usually replacing the valve is the easiest fix.


Hope this information helps you to understand your pressure situation

lbeachmike

Hi Ed -

Thanks for taking the time to provide such a thorough explanation. I would have to re-read this at night with a clearer head, though from my quick read it sounds like my symptoms more likely point to a faulty PRV than expansion tank?

It sounds like the pro's in my area likely do not troubleshoot because of the high value of their time - so it is likely the same cost for them (and thus for me) to replace both the expansion tank and PRV than to take time to troubleshoot?

Whatever my plumber did last October, did bring the system pressure down to 12 PSI for many months. It seems to have only climbed higher more recently. Doesn't that suggest that the expansion tank is likely okay? Our boiler runs year-round since it also handles the hot water.

I don't currently have the bandwidth to DIY this, so I am just looking to make sure that my plumber or heating company do the right thing in one visit - and to decide who of the two will be best to use for this.

Thanks.

Mike

EdTheHeaterMan

Properly maintained Expansion tank will last up to 10 years or longer. If your tank is older than 10, then replace it. the PRV performance is based on how often it might add water and the condition of your water. If you have lots of minerals or use a water. system that adds chemistry to provide a better water quality, then your valve can get a build up and pass water in as little as 3 years or less. If your on city water and have a decent quality water the PRV can last much longer.


The proper test is easy for a pro that understands the system. Some of the larger firms that offer you a Good Better Best repair scenario will tell you to replace all three parts that can cause the problem. Relief valve, PRV and Tank as part of their "Best" choice.


Since you also heat your potable water with your boiler, there is one more possibility, (Not likely with the conditions you described but still a possibility). The domestic hot water heat exchanger (Coil) could have a pin hole that is allowing water to pass from the high pressure potable water to the low pressure closed system boiler side. If that were the case, the fix from last year would not have worked. and you would be getting a constant pressure relief discharge.

That is why testing is the only way to be sure what component is the problem. If they don't test and just randomly shoot the parts cannon, that can get expensive. When they suggest a fix and give you a price. ask if that repair is guaranteed to solve the problem. Get it in writing if they say yes. Then if it is a different part, you may get it for free!

You should not have to pay for something that does not solve the problem. The service provider should absorb that cost. Call it the cost of education.

lbeachmike

Is there any reason to change the relief valve when changing the expansion tank and feeder valve?

It seems the tank is bad. All of the plumbers here seem to simply change all three rather than troubleshoot - but I witnessed the relief valve releasing water at 30 PSI, so there is no reason for me to believe it is bad.

Jamie Hall

The logic behind changing the relief valve is that they are cheap, relatively speaking, and they can fail to close properly when they have been operating, particularly when the are operating on low flows.