Normal pressure swing for hot vs cold?

Reply

  #1  
Old 01-30-17, 10:02 AM
V
Member
Thread Starter
Join Date: Dec 2016
Location: United States
Posts: 35
Received 0 Votes on 0 Posts
Normal pressure swing for hot vs cold?

I have a Buderus GB142, 2 story house, boiler in the basement.

The pressure on the manifold was reading 20psi cold.
The boiler's sensor reads lower, and it showed 12psi.
The GB142 shuts down at 12psi, so I adjusted the pressure regulating refill valve, which bumped the manifold pressure to 22psi, and the GB142 showed 14psi and started up.

Once it finished reheating the DHW and heated all three of the baseboard loops, the manifold pressure gauge shows 33psi, and the GB142 is reading 26psi.

I bought an additional gauge following the sticky'd post and attached it to a couple of the drain fittings to compare... it reads 32psi on the other end of the manifold (where the drain fitting is), reads about 26psi inside the zone 1 loop (before the zone pump), and about 33psi after the pump.

Questions I have:
1. Is 30psi the absolute max after which things might break, or is it safe to run at this pressure long term? A new boiler sensor is $100, and the boiler's max pressure rating is 50psi.
2. Is an 11psi swing normal for cold vs hot? Shouldn't my pressurized diaphragm tank be absorbing this swing? (Watts ETX-30)
3. Do I have something else going on?

I have not attempted to service the expansion tank or air extraction thingies. There are signs of corrosion at both of the air extraction valves, which makes me wary to touch them and cause a leak.
 

Last edited by vilord; 01-30-17 at 11:48 AM.
  #2  
Old 01-30-17, 02:56 PM
G
Member
Join Date: Oct 2008
Location: USA
Posts: 3,005
Received 13 Votes on 13 Posts
I suspect that your expansion tank is waterlogged. And, as you suggested, your boiler gauge should be replaced.
 
  #3  
Old 01-30-17, 05:07 PM
S
Member
Join Date: Oct 2013
Location: United States
Posts: 3,095
Received 61 Votes on 57 Posts
V,
From 14 to 26 is a big swing and as gil said. I would look at your extrol tank. Sounds like bladder problems. It either lost its charge or the bladder let go, filling the tank with water.

Probably the quickest way to check it is the tap test. With a screwdriver tap the top and it should sound solid, bottom should be hollow. Water enters the top and the bottom has the air charged diaphragm. That will not tell you what's wrong but it will tell you the tank is full and you have a problem.

To get a proper air pressure reading you must isolate the tank from the system or depressurize the whole system. In your case tap will be fine to start. Do this when the boiler is cold and then when it's running and hot. If you check the charge without isolating it the gauge will read system pressure which will not be an accurate reading.

As far your different readings it will always be higher after the pump. The pump increases the pressure but that's not the one your interested in unless you're having pump troubles. Go by the pre pump readings or the 14 PSI.
For the high pressure running concern, nothing will break but at 30 PSI the relief valve will let go to relieve excess pressure which may activate the auto fill valve to feed in fresh water which will bring air with it which may cause future circulation problems not to mention fresh water is the boilers worst enemy.

Hope this helps a little.
 
  #4  
Old 01-30-17, 09:41 PM
V
Member
Thread Starter
Join Date: Dec 2016
Location: United States
Posts: 35
Received 0 Votes on 0 Posts
Hmm. expansion tank sounded like it was hollow on the bottom, and filled at the top, so I tried draining off water until the boiler pressure read zero, per the instructions... it kept climbing back up again, took quite a few tries to get it to read zero and stay there, and i think i let some air in at the same time, shoot.

Checked the tank pressure, it was 13psi. System pressure is nominally 15psi or a bit higher, so i hooked up my bike pump to add a couple pounds... it climbed all the way up to 12psi... great, my bike pump is broken.

opened back up the refill circuit, and no additional pressure, no sound of water. tweaked the little arm on the top of the refill valve, and pressure slowly climbed up to 20, and kept right on slowly climbing until i turned the arm on the refill valve back again (we're talking maybe 3 degrees of rotation).

turned on the pumps, and i definitely heard some air moving about, but it maintained the 20psi charge.

i tried unscrewing the cap on the air extraction valve thing, which based on the image is a taco hy-vent or similar, but unscrewing it further had no effect. I'm hoping it is bleeding air, but have no way to check that i can tell.

I'm ordering a replacement boiler pressure sensor, since even with the pumps all off, the boiler is reading 5-7 psi less than both of the other gauges.

EDIT: looked at the pressure relief valve and realized that i've been turning the fast fill valve, not the pressure regulator adjustment screw. this explains a few things.
 
  #5  
Old 01-31-17, 08:45 AM
D
Member
Join Date: Apr 2014
Location: us
Posts: 984
Received 35 Votes on 33 Posts
Inaccurate pressure gauges are common.

The first thing to do is verify the hydronic pressure with a temporary pressure gauge. Easy way is using existing hydronic system drain valve with 3/4" male fitting.

Put together a gauge and a 3/4" female garden hose adapter with female NPT thread. First open valve and drain out debris. Attach to drain and open valve. Compare readings.

https://www.amazon.com/Dixon-Brass-F.../dp/B00BG1VQH8

Several years ago I put a post on this and NJT posted one. Could not find either.
 
  #6  
Old 01-31-17, 08:58 AM
V
Member
Thread Starter
Join Date: Dec 2016
Location: United States
Posts: 35
Received 0 Votes on 0 Posts
Thanks Doug
Here's the one that NJT posted, it is stickied in this forum:
http://www.doityourself.com/forum/bo...ure-gauge.html

I followed that and it agreed with the analog gauge on the manifold. Two against one tells me that the boiler is wrong. New sensor ordered.

I think the main problem I ran into is that i was increasing the system pressure by overtightening the fast-fill valve on the pressure regulator, rather than actually adjusting the pressure regulator.
-Jesse
 
  #7  
Old 01-31-17, 11:43 AM
S
Member
Join Date: Oct 2013
Location: United States
Posts: 3,095
Received 61 Votes on 57 Posts
V, it sounds like you might have a Taco feed valve. If you do then to use the fast fill feature you only have to lift the lever and not turn anything. That piece you're turning is the cap that houses a rod that pushes down on the diaphragm when the lever is raised for fast filling and when removed exposes the rod and adjusting screw.

To permanently raise boiler pressure you loosen the locking nut and turn clockwise, to lower go CCW and tighten nut when to lock and replace rod and cap when done.

As far as air is concerned if it wasn't much the vent on air scoop might take care of it. Remember to leave the cap on the vent loose for self venting. Tighten only if leaking until replacement.
 
  #8  
Old 01-31-17, 12:10 PM
V
Member
Thread Starter
Join Date: Dec 2016
Location: United States
Posts: 35
Received 0 Votes on 0 Posts
I have a watts 1156 style regulator. i loosened the locknut and turned the handle on top, instead of turning the sleeve.. so apparently I was just pushing the metal rod down... or maybe the valve is bad...

I'm going to try this again, draining down to 10psi and then turning just the sleeve part, and see if i can get it to self-regulate to 22psi (higher than i technically need, but i'm going on vacation and don't want it to shut down again before the boiler sensor is replaced.

I'm going to follow what was suggested here: http://www.doityourself.com/forum/bo...ine-valve.html
 
  #9  
Old 01-31-17, 12:23 PM
S
Member
Join Date: Oct 2013
Location: United States
Posts: 3,095
Received 61 Votes on 57 Posts
V, my mistake, I was thinking Watts and printed Taco. To adjust pressure leave the locknut tight and take the cap right off exposing the screw. Lift out the rod and the loose the nut and turn the screw clockwise to increase pressure. Tighten nut and replace rod and cap.

Skip
 
  #10  
Old 01-31-17, 12:48 PM
V
Member
Thread Starter
Join Date: Dec 2016
Location: United States
Posts: 35
Received 0 Votes on 0 Posts
Thanks Skip, just did this, I first dropped the pressure to about 15psi, then turned the screw in until i could hear a little water flowing, waited about 5 or 10 mins until it stopped flowing, around 18psi... turned in another quarter or half, it equalized at about 20psi, and the boiler now reads 15. Locked things down there and fired the boiler, it has gone from 70 degree water to 140 degree water and the pressure has only climbed about 1psi. Yay!

I think I can call this (temporarily) fixed!
I'll swap out the boiler pressure sensor when it arrives, and then I can ponder how much the deities are smiling on me as I wait until spring to loosen, clean, and re-tighten the currently leaky dielectric union that was the original cause of the pressure loss (doing the same thing as this: Buderus Header Manifold Leaking & Corroded €” Heating Help: The Wall)

-Jesse
 
  #11  
Old 01-31-17, 01:00 PM
S
Member
Join Date: Oct 2013
Location: United States
Posts: 3,095
Received 61 Votes on 57 Posts
Jesse, relax and have a good vacation. It will be here when you get back.

Skip
 
 

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