pressure relieve valve drops water after servicing expansion tank

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Old 03-05-13, 10:32 PM
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pressure relieve valve drops water after servicing expansion tank

We have a hydronic boiler in our two storey house with the single warming zone. The boiler was installed about 5 years ago, but since we did not have any problems with it, we did not realize we have to do annual maintenance.

Recently, we noticed drops of hot water from the drip leg going from the pressure relieve valve. It was leaking more towards the end of the active cycle, when the pressure-temperature gauge was showing higher pressure close to 28 psi. From this forum, we learned that our expansion tank may be water logged, and this might be the reason for what we observe. We checked the pressure in the expansion tank: it was at 0 psi, so the expansion tank lost all its air. Then we followed your instructions from another post to drain the expansion tank. Recommendations posted by NJ Trooper are very useful, thanks. To begin we tried to close the incoming water valve, but when we drained water a bit from the boiler, we noticed that water was still flowing into the system. Apparently, the water valve does not function properly. For this reason, we closed the main city water line. Next, to avoid draining upper floors, we turned off the valves on the return and outgoing lines (places where these pipes are connected to boiler are marked with “IN” and “OUT”). We also closed the bypass valve. After this, we turned on the drain valve, but stopped when the pressure in the system was zero. We used a small compressor to pump air into the expansion tank. We did a few iterations, as was recommended by NJ Trooper. At the end of this procedure the pressure was 12 psi in the ET and zero in the boiler. In the process, we observed leaking water through opening in the back flow preventing valve. Actually, it was dripping, not leaking. Is it normal? Why water would be leaking from there? What is the purpose of that opening in the backflow preventer valve? After this, we opened all valves completely and turned the thermostat on. The boiler started to work just fine. We observed that a sound of the working boiler has slightly changed. Before it was roaring with lots of mechanical noise, and water pipes around the house also made noise. Now the boiler is more quiet, but it sounds a bit differently with a slight high-pitched component. Also, one of the rooms that used to be cold feels warmer thanks to hot water in baseboards. Initially, the pressure in the system was around 20, but gradually it started to rise to around 24 psi.


The pressure relieve valve did not leak at all for several hours after draining the expansion tank. From this we conclude that the pressure relief valve by itself is fine, since otherwise, it would leak all the time. We did not touch it at all. The tank sounds hollow at the bottom as it should, but at the top there is some hot water, since the upper side is warm when you touch it. So, the expansion tank seem to be fine as well. But in the morning, we noticed that water drops slightly from the drip leg. Not so much, as it was before, but it looks like we still have some problem. Yes, we know, we emptied the expansion tank, but apparently something else is wrong in the system. The pressure in the system remains to be somewhat high. When the boiler stops its heating cycle, at this moment the pressure can be around 26-28 psi, and it never drops below 20psi. Any ideas? Please recommend what we can check to diagnose where the problem is coming from. Should we try to regulate the balancing bypass valve, and may be close it slightly? Our guess is that extra pressure from the outgoing line gets transmitted back to the return line, and as a side effect this causes the pressure-temperature gauge to show higher than normal pressure. Otherwise, perhaps, the pressure reducing valve does not do its job properly, but how we can check it?

We can send pictures, if this helps. Thanks in advance for comments.
 
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Old 03-06-13, 05:58 AM
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In the process, we observed leaking water through opening in the back flow preventing valve. Actually, it was dripping, not leaking. Is it normal? Why water would be leaking from there? What is the purpose of that opening in the backflow preventer valve?
They aren't 'supposed' to drip at all. They often do. When there are pressure changes on the valve and the parts 'move', they will sometimes leak for a day or three. The valve may stop leaking by itself and not require anything further.

The purpose of this valve is to prevent the boiler water from flowing into the domestic supply when the pressure in the boiler is greater... for example, when you turn the city supply off. Very basically there are two one way check valves and another intermediate valve that opens to the atmosphere if the outlet pressure is greater than the inlet pressure.

There is a diagram in this thread that shows the inner working of the backflow preventer valve if you are interested in the technical aspect:

http://www.doityourself.com/forum/bo...ater-line.html
 
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Old 03-06-13, 06:03 AM
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We observed that a sound of the working boiler has slightly changed. Before it was roaring with lots of mechanical noise, and water pipes around the house also made noise. Now the boiler is more quiet, but it sounds a bit differently with a slight high-pitched component. Also, one of the rooms that used to be cold feels warmer thanks to hot water in baseboards.
Recharging the expansion tank should not have made a difference with the sound of the boiler... It could have helped with the air noises in the piping... are you sure it's not just a 'perception thing' ? I can't think of any reason why there would be a quieter combustion or mechanical after this.
 
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Old 03-06-13, 06:19 AM
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The pressure in the system remains to be somewhat high. When the boiler stops its heating cycle, at this moment the pressure can be around 26-28 psi, and it never drops below 20psi. Any ideas? Please recommend what we can check to diagnose where the problem is coming from. Should we try to regulate the balancing bypass valve, and may be close it slightly? ........... Otherwise, perhaps, the pressure reducing valve does not do its job properly, but how we can check it?
I would say that there could very possibly be a problem with the pressure reducing valve.

The way you would check this is to close the manual shutoff valve after you have pressurized the system to nominal 12-15 PSI cold... then run the boiler with the water supply shut off for some time. If the pressure is now under control, you have found the problem that the reducing valve may be 'leaking through'.

Since your manual shut off valve isn't, you would first need to repair that in order to do this test.

I don't usually find that attempting to adjust a defective valve provides any help at all.


Our guess is that extra pressure from the outgoing line gets transmitted back to the return line, and as a side effect this causes the pressure-temperature gauge to show higher than normal pressure.
No, not at all...
 
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