help for a leaking boiler pressure relief valve?


  #1  
Old 12-04-09, 09:01 PM
A
Member
Thread Starter
Join Date: Dec 2009
Location: montana
Posts: 6
Received 0 Votes on 0 Posts
help for a leaking boiler pressure relief valve?

hi--i have an old 6 unit apt building with a 4yo burnham boiler, 300k btu nat gas. the old pipes and cast iron radiators are heating fine, but the boiler keeps dripping from the pressure relief valve at run temps (set at 30 psi, starts to leak at 32). No drips when boiler is off.

i replaced the valve and replaced the pressure reducer (12 psi) and check valve . the expansion tank is new and not waterlogged. i went up to the 3rd floor apts and installed air bleeder valves on the highest radiators, so i don't have a significant air build up in the radiators. i checked the others, and found no air. valve only drips at hi temps.

building is heating fine, and taco circulating pump seems to be pushing the water around. cold temp on the system is about 9-12 psi. looks like i'm losing about 2 gallons per day from the system. i'm worried that i'm increasing corrosion by daily adding fresh water into the system.

I can only guess at the possible problems. either the 190 temp is too high or maybe the circulating pump is too small? there are some old 4" heat mains on the system, so there's alot of water in the system. or maybe someone is much smarter than me and has a better idea......

any ideas? its going to be 12 below monday night, so i'm sure the boiler will be working hard!

thanks much!
 
  #2  
Old 12-05-09, 01:21 AM
B
Member
Join Date: Jun 2009
Location: Fairbanks Alaska
Posts: 92
Received 0 Votes on 0 Posts
Sorry, I am not sure what you mean.
Now with the new pressure reducer at 12psi, does the pressure relief still leak?
You are still losing 2 gal per day. Does that mean from the relief valve?

If the pressure hot is still increasing to over 30psi, that means that your expansion tank is too small.
 
  #3  
Old 12-05-09, 02:28 AM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,538
Received 7 Votes on 5 Posts
I think I'm going with Bilbo on this one that the expansion tank is too small.

A six apartment building likely has LOTS of water in the system (you said some mains are 4" ! ) and as such is going to need LOTS of room for expansion.

What size expansion tank is fitted?

Also, you said the pressure cold is 9-12 ? How tall is the building? That doesn't sound like enough pressure to me. NINE PSI is only adequate for a building that is around ten feet tall. Even 12 PSI is only going to get you to maybe 15-16 feet.

Along with the height of the building, it might mean that you in fact might need MORE than a 30 PSI boiler...

The height of the SYSTEM is actually what needs to be known here, from the bottom of the boiler itself, to the highest point in the system.

If for example, you tell us the system is three floors, and 30' from the boiler to the highest radiator, the MINIMUM pressure when cold in that system would have to be SEVENTEEN PSI.

Then, your expansion tank would need to be sized so that the system pressure did not exceed 27 PSI.
 
  #4  
Old 12-06-09, 09:13 PM
A
Member
Thread Starter
Join Date: Dec 2009
Location: montana
Posts: 6
Received 0 Votes on 0 Posts
xpansion tank is an Amtrol 60, does not feel waterlogged at all. If i take a pressure reading on it, should i do it hot or cold?
 
  #5  
Old 12-06-09, 09:33 PM
A
Member
Thread Starter
Join Date: Dec 2009
Location: montana
Posts: 6
Received 0 Votes on 0 Posts
Thanks for the help! bottom of boiler to top of the highest radiator is about 24 feet.

pump is a Taco12-f4. it says it has a head range of 0-14.5 feet. but in a closed loop system, isn't the return water falling just as hard as the hot water has to rise? I didn't think head calcs really mattered--only friction calcs, and I wouldn't have the first clue as to calculate system hydraulic friction.

But Even at $300 for a new pump or $150 for a larger expansion tank, i could swap that out cheaper than I can get a plumber just to show up.

If the AMtrol 60 is too small, can I add a second expansion tank, or do i need to replace that one?
 
  #6  
Old 12-07-09, 01:52 AM
F
Member
Join Date: Mar 2006
Location: Wet side of Washington state.
Posts: 18,495
Received 36 Votes on 28 Posts
You do not have to replace the existing expansion tank, you may add additional tanks. Remember that you can easily have too small of an expansion tank but never too large an expansion tank.

With big pipes and cast iron radiators you do have a large amount of water in the system. I'm fairly confident that the single #60 expansion tank is woefully inadequate.

Also, air in the radiators would not be a cause of excessive pressure excursions, just the opposite as the air in the radiators would act as additional mini expansion tanks. Bleeding the air from the radiators was absolutely the correct thing to do but if there was a significant amount of air it would have masked the problem of a too small expansion tank.
 
  #7  
Old 12-07-09, 03:46 PM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,538
Received 7 Votes on 5 Posts
Amtrol 60, does not feel waterlogged at allAmtrol 60, does not feel waterlogged at all
Any testing done by 'feel' or tapping for 'sound' are not conclusive tests.

If i take a pressure reading on it, should i do it hot or cold?
Hot or cold doesn't really matter. What DOES matter is that the water side of the tank is at ZERO PSI. You can not take an accurate pressure reading on the tank when it is installed on a system that has any pressure on it. You will NOT get an accurate reading.

Your tank(s) should be charged to the same air pressure as the cold fill pressure, in your case 15 PSI.

To get an accurate reading on the tank air charge, you must first drop the system pressure to ZERO. Then, and only then, will the air charge reading on the tank be accurate.

If you find the pressure to be low in the tank, add air to 15 PSI, then check the boiler gauge again. If it has come off ZERO, drain more pressure from the system back to zero again, and recheck the tank pressure. Add more air to the tank, and check for zero on the boiler again. When you have 15 PSI in the tank, and ZERO on the boiler, you can go ahead and re-pressurize the system.

You do NOT have to completely drain the boiler. Only let out enough water to drop the pressure to zero, and close the drain.

bottom of boiler to top of the highest radiator is about 24 feet.
24 X 0.432 = appx 10.5 PSI, now you ADD 4 PSI for 'headroom' to assure that the the top of the system is always under a minimum pressure with the system COLD. Your system should have a COLD FILL PRESSURE of 15 PSI MINIMUM.

isn't the return water falling just as hard as the hot water has to rise? I didn't think head calcs really mattered--only friction calcs,
Absolutely correct. It's a big 'ferris wheel' inside your pipes. So there is no 'uphill struggle' such as a well pump might have. But, in a closed system, HEAD and FRICTION are the same thing. RESISTANCE TO FLOW is the bottom line. I'm sure your pump is fine.

Here's a link to an Amtrol brochure with some good info on how the tanks work, how to size them, etc:

Amtrol EXTROL data

Without knowing the volume of water in the system, you kinda have to go by educated guesswork in sizing the expansion tank. As furd said, it's better to err in sizing the tank larger than you need because larger won't hurt a thing, too small is the problem. I might be inclined to suggest adding a second tank.

A floor standing tank such as the SX-30V will probably be easiest to install if you have space for it. Yes, it's a little pricier than the hanging models... you can place it where you have room, and pipe it to where the existing tank is connected, install a tee, hang the existing tank from the tee, and run the new tank to the side of the tee.

A couple extra optional items when you are doing the work will make life a LOT easier:



With the added isolation valve and drain you can now very easily check/adjust/change the tank(s). Close the isolation, drain the pressure from the tanks, add air easily without having to touch the boiler.

When not in use, REMOVE THE HANDLE from the isolation valve and hang on a nail near the boiler. This will keep curious hands from accidentally closing the valve.

After you get the tank situation straightened out, you need to determine why your pressure is going down to 9 PSI at times. You want to maintain at LEAST 15 PSI COLD at all times in a 24 foot tall system.
 
  #8  
Old 12-18-09, 07:40 PM
A
Member
Thread Starter
Join Date: Dec 2009
Location: montana
Posts: 6
Received 0 Votes on 0 Posts
ok--made it through the cold snap. when the temp hit 40 I dove in on the boiler. added a second amtrol 60 with an isolation valve and drain. changed out the old 30psi relief valve too. tank is precharged to 12 lbs. first tank still seems ok, i think. its only 3 yrs old. cold boiler pressure is 12 pounds. After the boiler runs for a while, it is still creeping up on 30 psi. It did drain a small amt from the new relief valve, but significantly less than before. Temp is at 190. Would a cooler temp help? What's next?
 
  #9  
Old 12-18-09, 08:14 PM
esalman's Avatar
Member
Join Date: Nov 2008
Location: United States
Posts: 203
Received 0 Votes on 0 Posts
Is the aquastat set to 190 or the gage is reading 190. If the stat is set to 190 the water temperature will over shoot closer to the boiling point. Lower temperature = less expansion. Bring the temperature down to 170, If it helps you can wait for warmer weather to tinker with it.

Beer 4U2
 
  #10  
Old 12-19-09, 08:04 AM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,538
Received 7 Votes on 5 Posts
Andy, either the first diagnosis of too small a tank was wrong, or your 'Pressure Reducing Valve' that feeds the water into the system is leaking... OR a combination of problems...

There should be a manual shut off valve on the feedwater line, ahead of the pressure reducing valve.

Let the boiler cool to 100 or so... set the pressure in the boiler to 12-15 (drain a little off if it's too high, or add if too low), and then CLOSE the manual water feed valve. Run the boiler up to temperature and check the pressure.

If the pressure remains under control with the manual feed valve closed, it means that your reducing valve is leaking through, and should be replaced. You can run the boiler with that valve closed as long as you keep an eye on the pressure gauge from time to time. If you are diligent, you can wait to do the repairs...

One other remote possibility is that if your boiler heats domestic water via a 'tankless coil' inside the boiler, that coil could be leaking into the boiler... Not sure if we asked how your domestic is being heated... don't think you do have a coil... but for completeness, that's the last thing the problem could be.
 
  #11  
Old 12-19-09, 09:35 AM
A
Member
Thread Starter
Join Date: Dec 2009
Location: montana
Posts: 6
Received 0 Votes on 0 Posts
nope, no boiler mate. Domestic hot water is totallty separate. I already replaced the expensive pressure reducer/anti-bckflow valve, and that didn't fix it. I'll try putting the aquastat at 180 instead of 190. It seems that the pressure doesn't build that high until the system has been running for a few hours. I have a programmable thermostat, and I'll set it closer to a steady 24-hr temp so the boiler wont have such a big temp delta to overcome when it kicks back on. Running out of ideas. thanks for all your help.

andy
 
  #12  
Old 12-19-09, 10:15 AM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,538
Received 7 Votes on 5 Posts
I already replaced the expensive pressure reducer/anti-bckflow valve, and that didn't fix it
I see you said that in your first post... didn't re-read (as usual!).

I would still recommend that you do the test of closing the manual feedwater shutoff valve. It IS possible that the new valve is somehow defective... a piece of 'crud' could have gotten stuck in the new valve... the incoming water line should always be flushed out before installing a new valve, and if it wasn't, well, ya might have a new valve that's leaking... there was another thread here recently where exactly that happened.

Troubleshooting is all about KNOWING, not GUESSING.

Last straw to grasp at is that your pressure gauge is toast.
 
 

Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: