Boiler pressure question


  #1  
Old 10-19-14, 06:00 PM
B
Member
Thread Starter
Join Date: Oct 2014
Location: US
Posts: 5
Received 0 Votes on 0 Posts
Boiler pressure question

I recently installed a new Watts 1156 pressure reducing valve/auto feed on my boiler.

When I first installed, the cold pressure rose to about 20 PSI (the instructions say these are preset to 15 PSI). I used another gauge to verify the accuracy of the boiler gauge (that you use to test the house pressure from an exterior spigot) and I was getting approximately the same reading (few PSI less).

I adjusted the PRV by turning the screw counterclockwise a couple times. I drained some water and let the valve refill. I'm now getting about 11 PSI.

My house is 2 stories and approximately 20 ft from the basement floor to the top of the 2nd story rads. Based on this, I need about 12 PSI minimum.

My question......if the pressure was set a little too low (let's say the true reading was 10), would I not get any heat in the 2nd floor rads? Right now, I'm getting heat upstairs, so I was planning on leaving the PRV setting alone. Any issues in doing that? (does low pressure suck air in the system, but strain on the system, etc?)

Second question........the Watts 1156 says the set range is 10-25. Does this meant that no matter how much you turn the adjustment screw counterclockwise, the system should never be below 10, correct?
 
  #2  
Old 10-19-14, 06:03 PM
B
Member
Thread Starter
Join Date: Oct 2014
Location: US
Posts: 5
Received 0 Votes on 0 Posts
Forgot to mention......I'd like to keep the initial PSI as low as possible because the pressure rises about 10 in the system (currently about 12 - 21). I thought it was a bad expansion tank, so I replaced that. Same result.

I think it may be just a large system (12 large cast iron rads, 6 baseboard cast iron rads) and a somewhat undersized expansion tank (Extrol 60)

Might change this eventually, but right now I just want to make sure I'm not potentially causing more issues by dropping the pressure too low
 
  #3  
Old 10-19-14, 07:34 PM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,539
Received 4 Votes on 3 Posts
That gauge that you used to verify... probably 150 PSI range? You can't count on it to be accurate at that low of a pressure, but still, you said it indicated a few PSI lower than the boiler gauge?

So, based on those facts, is it not possible that the new valve was in fact setting the system at 15 PSI?

My experience with boiler gauges is that the accuracy gets progressively worse the higher the pressure in boiler goes. So, if you were reading 20 (which might have really been 15) as the pressure climbed, it would probably not have shown LINEARLY on the gauge. In other words, maybe it really did start at 15 and only climbed 8 and not the 10 you believe it did.

if the pressure was set a little too low (let's say the true reading was 10), would I not get any heat in the 2nd floor rads?
Hard to say... if the system is and was relatively air free, you would still get circulation and heat. When the boiler cools down is when the problems start. The upper parts go sub-atmospheric and any air in the water will get pulled out and form bubbles. It might take days... maybe weeks... but you would start to hear air circulating... particularly if you don't have decent air removal devices.

Remember that when the system is HOT, your pressure is adequate. It's when it's COLD that you won't have enough pressure.

the Watts 1156 says the set range is 10-25. Does this mean that no matter how much you turn the adjustment screw counterclockwise, the system should never be below 10, correct?
No, probably not. They probably mean that the valve is only ACCURATE in that range. Part of accuracy is REPEATABILITY. It might work at a lower pressure, but it won't work well. (I've tried it myself by the way, it never went to zero, but it did go below 10. It was not REPEATABLE though.)

(currently about 12 - 21)
There's nothing at all wrong with 21 PSI. It's when you get to 27 PSI that you have to start thinking about making some corrections. You had plenty of 'headroom' at 21 PSI.

I think it may be just a large system (12 large cast iron rads, 6 baseboard cast iron rads) and a somewhat undersized expansion tank (Extrol 60)
I think so too. But as long as you keep the low end at 12, and the expansion tank properly charged, pressure going to 21 is NOT a problem.

What I would do if I were you is get a smaller range gauge and verify the boiler gauge not only at cold fill, but also at the higher HOT pressure. I bet you are going to find that the HOT pressure is not as high as you believe it is and that the boiler gauge is not linear and has progressively more error as the pressure increases.

Have you read both of these threads?

http://www.doityourself.com/forum/bo...ure-gauge.html

http://www.doityourself.com/forum/bo...sion-tank.html
 
  #4  
Old 10-20-14, 06:23 AM
B
Member
Thread Starter
Join Date: Oct 2014
Location: US
Posts: 5
Received 0 Votes on 0 Posts
Thanks Trooper

Yeah, the more I think about it, the more I think the gauge might be reading a little high. I've looked around for a lower range PSI gauge and no one seems to carry them (even checked the plumbing supply store locally and they didn't have one). I plan on stopping by the pool supply house next, maybe they have one

I've definitely hearing the water in the pipes (which likely means air), but there's been work done on the system lately so I'm sure a ton of air got introduced into the system.

It's strange though......when the boiler was cold, the gauge was reading 11-12. Let's assume that wrong by 3-5 (which means the actual boiler PSI was 8 or 9), I don't understand why I would still get heat in the second story rads. I would think the PSI would be too low.
 
  #5  
Old 10-20-14, 08:08 AM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,539
Received 4 Votes on 3 Posts
Let's assume that wrong by 3-5 (which means the actual boiler PSI was 8 or 9), I don't understand why I would still get heat in the second story rads. I would think the PSI would be too low.
As long as enough air hasn't collected up top to actually block the flow, you could still have flow. With the pipes all full of (mostly) water, it would still pump through, even if the pressure up top is zero, or sub-atmospheric. Think 'ferris wheel'.

In time though, enough air could/would collect that would stop the flow.
 
  #6  
Old 10-20-14, 08:25 AM
B
Member
Thread Starter
Join Date: Oct 2014
Location: US
Posts: 5
Received 0 Votes on 0 Posts
One other item that may or may not matter......

When I open the bleeder valves on the top of the 2nd floor rads, I'm getting a solid stream of water. I would think if the pressure was very low or zero, I would get nothing coming out or a dribble (when boiler is cold), correct?
 
  #7  
Old 10-20-14, 09:32 AM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,539
Received 4 Votes on 3 Posts
When I open the bleeder valves on the top of the 2nd floor rads, I'm getting a solid stream of water. I would think if the pressure was very low or zero, I would get nothing coming out or a dribble (when boiler is cold), correct?
Yep. So maybe you have enough pressure...

Gauges are pathological liars.
 
  #8  
Old 10-20-14, 05:04 PM
B
Member
Thread Starter
Join Date: Oct 2014
Location: US
Posts: 5
Received 0 Votes on 0 Posts
Okay Trooper....so I bought a test gauge today. 0-60 PSI was the lowest I could find.

Hooked it up to the boiler drain tonight and here's what I got....

Cold - Boiler 15, Test Gauge 14

Full Temp Hot - Boiler 25, Test Gauge 22

So, looks like the boiler gauge is a little off, but like you said, the hot seems to be off more then the cold (10 PSI rise on boiler gauge vs. 8 PSI rise on test gauge).

Bottom line, both the cold start and hot PSI seem reasonable to me based on a 2 story, cast iron system, correct?
 
  #9  
Old 10-20-14, 05:12 PM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,539
Received 4 Votes on 3 Posts
Bottom line, both the cold start and hot PSI seem reasonable to me based on a 2 story, cast iron system, correct?
Yes, I don't see a problem with that at all.
 
 

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