old PressureTrol springs get weak?

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Old 03-24-15, 08:46 AM
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old PressureTrol springs get weak?

That seems possible, right? The cut-out spring that opposes the boiler pressure would eventually get weak, and so the Ptrol would trip off under too-light pressure. Also, the cut-in spring that pulls the relay back on when things cool down could eventually get weak and not be able to pull the relay back on as it normally should.

That seems to fit what happened twice on my old boiler back at the end of September 2014. I had to go down to the cellar each time and manually get the burner going again by fooling with the Ptrol. Both times, it happened during a tankless heating cycle - which normally runs for only about 5 minutes.

Nothing had been changed in the system that would cause the problem - no change in air valves or radiators, etc.

Then things worked fine until the beginning of January. The Ptrol tripped off twice on water heating cycles, and then once when the thermostat called for heat (about 1/2 hour into the heating cycle). This problem had never happened before this heating season.

At that point, I figured I'd better adjust the Ptrol a little to tighten up the springs: from 0.5 to about 1.5. The problem hasn't happened since. The differential is and has always been set at 2.

Does all that sound reasonable or is there another explanation? I ask because I want to understand what happened. I will probably replace the Ptrol when the weather gets warm. Thanks.
 
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Old 03-24-15, 09:53 AM
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Robb, I don't believe that the Ptrol is under control for tankless water heater calls. You should also have an aquastat set at perhaps 150-160 or so.

You may have a blockage in the pigtail siphon tube. This can cause over pressure if it's blocked and can't let the control 'see' the pressure, OR, it can also 'hold' pressure on the Ptrol and not allow it to sense the drop to fire the burner back on again.

Before condemning the Ptrol, check the obvious things first...
 
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Old 03-24-15, 10:50 AM
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R,
Your Ptrol reacts to steam pressure only, not water temp. for the tankless and therefore has no bearing on your boiler running for hot water. That is your aquastat.

By adjusting to Ptrrol cut-in point from 0.5 to 1.5 you have caused the boiler to come on sooner and short cycle.

Your Ptrol is your high [pressure] limit on your boiler. It only comes into play when the tstat doesn't get satisfied in time.

It only reacts to the settings, no matter what they are.

Ptrol operation: CUT OUT= CUT IN (0.5) + DIFFERENTIAL (2.0). Your boiler should cut out at no more than 2.5 psi.

By changing your cut-in point your boiler now starts at 1.5 psi and shuts off at 3.5 psi.
This does two things. 1) Slows down your steam delivery to the rads and 2) short cycles the boiler and starts it prematurely.

It is not the Ptrol that fails, it's the pigtail that gets clogged and must be removed and flushed As Trooper has stated. Sometime they get so bad you buy a new one. They are cheap money.

If you didn't throw your old Ptrol away yet, hang onto it, I bet it will work when you get the pigtail fixed.
Good Luck,
 

Last edited by NJT; 03-24-15 at 11:09 AM.
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Old 03-24-15, 11:14 AM
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1) Slows down your steam delivery to the rads
This seems counter-intuitive when first read... and it may be...

BUT the fact is that LOWER PRESSURE STEAM TRAVELS FASTER.

Google it and you will find long explanations of WHY... or just trust us (don't worry, we're not lawyers) that this is true.

OR, I'll save ya the trouble, read this, Dan Holohan is the BOSS when it comes to STEAM:

https://heatinghelp.com/systems-help...team-velocity/

Turn the CUT-IN back down to 0.5 and find the real problem.

In fact, turn the DIFF setting inside down to 1.5 while you're at it.

And clean out the pigtail.
 
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Old 03-24-15, 11:23 AM
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More required reading from Dan H.

Any homeowner with steam heat MUST read this book!

http://www.amazon.com/Got-Steam-Heat...s=we+got+steam
 
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Old 03-24-15, 03:20 PM
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Thanks to you both for your replies. I'm curious now about what I'll find when I go to clean out the pigtail - when the weather no longer is getting so frigid overnight. From your replies, it sure seems to be clogged.

Btw, when the Ptrol was tripped during a burn called by the aquastat... I should have mentioned that the thermostat was off at the time. Sorry.

From Holohan's comment on his article page:
Once a pigtail clogs, just about anything can happen. Much depends on how clogged it is.
I guess so.


I just did this as a test:
  1. turned cut-in back down to 0.5
  2. removed Ptrol cover and tripped it manually
  3. turned up aquastat and heard it click as it called for the burner to come on
  4. but the burner did not come one

So, at least on my 42 year old boiler, the Ptrol does prevent the aquastat from lighting the burner.

Thanks again.
 
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Old 03-24-15, 03:54 PM
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at least on my 42 year old boiler, the Ptrol does prevent the aquastat from lighting the burner.
If you want, after you check the pigtail, we can look into the wiring.

On the other hand... even though it may not be 'typical' wiring, if the Ptrol DOES cut out the aquastat when it reaches it's cut-out pressure... so what? If the boiler is hot enough to be cut-out on pressure, then there is no need for the a'stat to fire the boiler anyway, right?
 
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Old 03-24-15, 04:05 PM
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On the other hand... even though it may not be 'typical' wiring, if the Ptrol DOES cut out the aquastat when it reaches it's cut-out pressure... so what? If the boiler is hot enough to be cut-out on pressure, then there is no need for the a'stat to fire the boiler anyway, right?
Except that leaves the problem that it does not cut back in as it should (when cut-in is adjusted to 0.5).

The problem also occurs sporadically, which is odd.

If you want, after you check the pigtail, we can look into the wiring.
If theoretically the aquastat malfunctions and stays on permanently, shouldn't the Ptrol be wired to rightly cut out and prevent a problem?
 
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Old 03-24-15, 04:17 PM
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Except that leaves the problem that it does not cut back in as it should
Which might be fixed with the pigtail cleaning.

Can't rule out the Ptrol as a problem yet though. Gotta hit all the bases first.

If theoretically the aquastat malfunctions and stays on permanently, shouldn't the Ptrol be wired to rightly cut out and prevent a problem?
That thought did cross my mind. It would act as an 'auxiliary high limit' of sorts. Many juriscitions require an aux high limit on hot water boilers as well.

If cleaning the PT solves your problem, we're gonna leave it be.
 
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Old 03-24-15, 04:24 PM
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Okay, thanks.
..........................................
 
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