Slant-Fin Liberty Boiler,Pressure Issue,Relief Valve leaks

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Old 01-01-09, 11:09 AM
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Question Slant-Fin Liberty Boiler,Pressure Issue,Relief Valve leaks

I have a 4 year old Liberty II Boiler, when the system calls for heat and the circulator runs, the pressure of the boiler reaches right at 30 lbs and the watts 174, 30 LB relief valve starts to leak water about a cup per heat call. Water temp at 180.I have replaced the expansion tank with a slightly larger one and replaced the relief valve twice. I tried bleeding air. When it heats water with the internal coil it is fine and pressure never exceeds 15 lbs. Can I go to a slightly higher relief valve 35 lbs or so?? Any ideas?? What causes the pressure to rise close to 30??

After I went to the larger expansion tank it worked fine for 2 years. Checked the expansion tank again and it seems ok.
When I call for heat the boiler the fires and I watch the pressure slowly rise to just at 30 lbs and then the valve leaks a cup or so of water. When the boiler stops it drops back to a few pounds. Heating water with the internal coil, the pressure barely moves.
Replaced Expansion tank and relief valve twice and tried flicking the handle, Bleed air from the heat lines. This is a single zone setup for a small home.

Thanks
Tony
 
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Old 01-01-09, 01:35 PM
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How was the expansion tank sized in the first place? You need to consider all of the water stored in the boiler, piping, rads etc and have enough capacity so that the water has enough air to displace as it expands when it rises in temperature without ever hitting 30 psi. The easy way is not higher psi relief valves, it's having enough expansion tank capacity.
 
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Old 01-01-09, 03:42 PM
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Tony, when you check the air charge in the expansion tank, there must be ZERO pressure on the water side of the tank. If you don't drop the system pressure to zero, you can NOT get an accurate reading of the air charge in the tank. You will read the HIGHER of the two pressures.

In normal operation, an expansion tank will lose between 1 and 2 PSI per year due to air migrating through the membrane. Same reason that rubber kids baloons will slowly deflate over a few days...

So, shut the boiler off and let it cool to 100° or less. Hook up a drain hose, close the manual water feed valve, and open the drain to ONLY drain enough water so the pressure in the boiler drops to zero, then close the drain valve. Do NOT drain the boiler completely!

NOW check the air charge in the tank. It will be low. Pressure it back up to 12 PSI.

Re-check the boiler pressure gauge, if it has lifted off zero, open the drain again and run it back down to zero. Re-check the tank pressure and add more air if necessary to get to 12 PSI... LRR (Lather, Rinse, Repeat) as needed until the tank is at 12 with the boiler at ZERO.

Re-open the manual feed valve and verify that the boiler pressure comes up to 12-15 PSI and levels off. If it continues to rise past this point, your regulator is either out of adjustment, or leaking through.

Should be good to go ...
 
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Old 01-01-09, 10:00 PM
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NJ Tropper
I understand the concept and process, but what do I use to measure pressure in tank and what do I use to add more charge if needed?
 
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Old 01-01-09, 10:36 PM
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An accurate tire pressure gauge, and a bicycle pump (if yer strong) or a small air compressor with a tire air chuck.
 
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Old 12-06-09, 12:11 AM
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Same exact problem!!

Hey did you ever get your boiler to stop leaking? I have the same problem with my 5 year old Liberty II boiler. I replaced the Relief valve and the air expansion tank (checked the pressure when I installed it, and it was at 12 p.s.i.) and it still leaks. The pressure is at 32 psi when it is firing, and that is just enough to have it leak out of the 30 p.s.i. release value.
 
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Old 12-06-09, 10:05 AM
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If you are sure that the tank is correct, there are two other possibilites.

1. Your 'Pressure Reducing Valve' is leaking through and over pressurizing the system.

2. If you have a domestic hot water heating coil in your boiler, it could also be leaking pressure into the boiler.

#1 is more likely.

There should be a manual shutoff valve on the water line feeding the boiler. Close that manual valve, and open a drain valve on the boiler to let out the excess pressure until you have 12-15 PSI in the boiler when it is cold.

Run the boiler with the manual valve closed and watch the pressure. If it remains under control, you know the Reducing valve is leaking.

There is actually one more possibility... if you have an isolation valve between your tank and your boiler that you closed to change the tank, are you sure you opened that valve again when you were done?
 
 

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