Another Boiler Pressure Too High


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Old 12-23-14, 12:03 PM
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Another Boiler Pressure Too High

Reference this thread from which this post was moved:
http://www.doityourself.com/forum/bo...ml#post2364687

I'm sorry to hijack your thread, but I was about to post the same exact post. Hopefully we can help each other out, somehow.
The only difference we have is I don't have an indirect water heater. The pressure on the old boiler would rise to 30 psi causing the PRV to open. I replaced the PRV, new tank with valve, new aquastat. The pressure would still rise - even with the supply shut off which eliminated the need to replace the water feeder.

I was told to replace the boiler and so I did. Problem still exists. When I would adjust the pressure to 15-20 psi and the boiler is heating the water, pressure slowly creeps to 30psi. I spoke to Weil Mclain rep and he suggested to run the circulator pump and turning the gas off to see if the pressure rises - it doesn't. Pressure only builds up with the flame on.
Very confused and aggravated...
 

Last edited by NJT; 12-23-14 at 12:20 PM.
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Old 12-23-14, 12:27 PM
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I was told to replace the boiler and so I did.
Boy did you get some bad advice! I'm sorry you got taken.

What was the rationale they applied that somehow conviced you that the boiler itself was somehow at fault?
 
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Old 12-23-14, 12:36 PM
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Before the problem started, did you have a 'history' with this system and know it to have been operating properly at one time?

Is there any more 'back story' that you haven't yet told us?

If there is no domestic water heating, either an indirect water heater or a 'thankless coil' inside the boiler, then over pressure can only be two things.

Either the pressure reducing valve or the expansion tank is defective.

If the pressure holds when the water supply valve has been turned OFF, and the pressure still rises with heating, then the problem is in the expansion tank.

It's either improperly charged, or defective. OR it's too small for the system.

What type of heat emitters are installed in the home? Cast Iron standing radiators? Copper tube and fin baseboards?

What size is the expansion tank?

OR, there is another 'hidden' connection of city water to the system somewhere, and that valve is leaking. Inspect every single inch of piping around the boiler for another water feed.
 
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Old 12-23-14, 05:21 PM
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I agreed to replace the boiler as it was over 20 years old. Granted it could have worked another 20 if this pressure issue didn't "appear out of the blue"

No back story, really. Existing boiler developed the same issue and after replacing all the mentioned parts, it was agreed to switch the boiler.

Existing expansion tank was replaced with in kind. Then when the new boiler was installed, and the pressure issue still persisted. Expansion tank was upgraded to a #30 - that did not help.

Heat emitters are copper tube fin type. No other connection to the city water anywhere.

One thing to point out - the pressure only creeps to 30psi when the boiler heats the water from cold water condition and it reaches 30psi at around 160 degrees F. Once the preset temp of 180 is reached and the boiler is simply cycling, the pressure seems to remain at whatever I would set it to - usually 18-20psi.
 
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Old 12-23-14, 07:41 PM
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the pressure only creeps to 30psi when the boiler heats the water from cold water condition and it reaches 30psi at around 160 degrees F.
This really screams undersized, or incorrectly charged expansion tank.

The fact that you have fin-tube BB says that the 30 size tank is probably big enough.

This leaves improper air charge.

Read this for step by step instructions on correctly checking and charging the air in that tank:

http://www.doityourself.com/forum/bo...sion-tank.html

No other connection to the city water anywhere.
Absolutely positively certain? You have personally examined the entire system and know each and every pipe on a first name basis?

Once the preset temp of 180 is reached and the boiler is simply cycling,
What do you mean by 'preset temp' ? Are you saying that your boiler stays hot ALL THE TIME?

the pressure seems to remain at whatever I would set it to
Again, I don't understand what you are saying here... do you mean to say that the boiler gets hot and stays hot all the time and that you somehow are 'setting' the pressure? How are you doing that?

Can you take and post pictures of your installation please?
 
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Old 12-23-14, 08:41 PM
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Will check the pressure in the tank when I get home, but this was the second brand new tank so this makes me believe that the tank is not the culprit.

As far as other supplies, I am certain.

By preset temp I meant the high limit. The boiler doesn't stay ON all the time.
Here's step by step of what I've noticed:

1) With cold water in the boiler/system, the boiler fires and starts heating the water. Once the temp reaches around 160F, the temp starts slowly creeping from my preset 20psi to 30psi. At 180F the pressure just reaches 30psi. Flames are off and the circulator pump is running.
2) I drain some water (very very little is needed to drop it back to 20psi). The pressure stays at 20psi even the flames are back on.

I shut the boiler off and let the water cool overnight just to test and it again was proven that the pressure only rises when the boiler heats cold water.

I will post pictures when I get back home as well.
 
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Old 12-23-14, 08:59 PM
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this was the second brand new tank so this makes me believe that the tank is not the culprit.
Understood, but was the pressure in the tank actually CHECKED before being installed? I know that the factory SAYS they are precharged to 12 PSI, but lots of things can happen between their door and yours!

starts slowly creeping from my preset 20psi to 30ps
OK... so why are you STARTING at 20 PSI then?

Typically 12-15 PSI is where the boiler should be when cold.

Ten PSI increase from cold to hot is not out of the ordinary.

If you START at 12-15, you'll be fine!
 
 

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