Boiler Leak at Aquastat Dry Well

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Old 06-28-08, 11:33 AM
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Unhappy Boiler Leak at Aquastat Dry Well

I have a Buderus G234X-38 Boiler for radiant heat, baseboard, and DHW. I am getting a water/glcol mix slowly dripping out of the boiler. I have limited access, but it appears to be leaking at the immersion well fitting for the Honeywell L8148E Aquastat.

I am trying to figure out if I can remove the Aquastat to access. Honeywell manual is not clear. Any help?

I can probably get a wrench in from the side and try to tighten well, but don't know if I am going to torque or damage bulb element. ??

Also, I appear to be getting air into the system. While troubleshooting, I shut off supply and return valves to boiler for a couple of weeks. Expansion tank isolated from boiler. Pressure dropped from 14psi at 150degreeF to 0psi at 60degreeF on gauge at boiler.

Can the pressure go negative and suck air into boiler?

Is there a formula to calculate pressure change in boiler based on temperature change

Thanks,

FJ
 
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Old 06-29-08, 08:23 AM
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Hello
Is it leaking from inside the well or around the threads? If it is inside the well, it must be replaced. If it is around the threads follow the instuctions below.

If you are going to remove the aquastat well you will need to release the pressure and probably drain the boiler. Not something you want to do too often with a glycol system.

Here is what I would try. Turn off the power and water supplies. Then remove the control. There should be a screw to loosen, then the control with the bulb should be easily removed. I would close off any isolation valves for the zones, Heating and domestic hot water, and also the expansion tank if possible. Then I would drain the boiler to lower the pressure to zero,(should only be a little bit), and loosen the aquastat well as much as possible, without completely removing it. Then put pipe dope and teflon tape over the threads. Re-tighten well and you should be fine.
This should be done when the boiler is cooler so you don't get burned. If you feel you cannot do this, do not try. have a professional heating technician do it for you.



Typically the pressure for the boiler should be around 12-15psi when cold, for a standard 2 story home. The pressure setting on the tank is usually pre-set to 12 psi I think. When the boiler is up to temp and if the tank is working properly, the pressure should go up no more than about 5 psi. I am sure there is a chart or formula for this info, but I do not have it at this time. If it is going up to 30 psi, the tank is waterlogged or a valve is shut off. If the tank is staying at 30psi, something is filling the boiler like the fill valve, or a leak in the coil in the domestic water heater.

I have been told that air vents on the return side could in fact pull air into the system and for that reason, I have stopped putting them on the returns.

What kind of piping have you used? If you used PEX piping and it is not rated for "Heating" it may not have a full oxygen barrier and will allow air to penetrate through the pipes, or so I have been told.

A 14psi change in pressure is way too much and I would be checking the expansion tank. Maybe the bladder is junk and that is where the air came from.
You need pressure for altitude. If you have zero pressure the only place you can heat is the basement. If you have a 2 story home, you will need about 15 psi in the boiler at all times. If you look at the pressure gauge on the boiler, it should also show how much pressure is needed for altitude.
 
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Old 06-29-08, 10:28 AM
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More ideas on the pressure change...

Let's say that the auto fill valve is closed.

And the expansion tank is toast... bad bladder / no air charge.

The system pressure is adjusted when the boiler is hot to say 14 PSI.

When the system cools, the pressure will drop like a stone.

On the other hand, if the system were pressurized to 14 PSI when cold, and the boiler were fired, the relief valve would open around 30 PSI .

Two sides of the coin...

My guess is that the tank either has a bad bladder, or there is no air charge in it.
 
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Old 06-30-08, 02:46 PM
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Thanks for the input.

Question: Plumbing God - you said not to remove the well completely. What is the reason for this?

To be clearer, the pressure in the boiler drops from 14psi within the boiler to zero when the internal boiler temp. changes from 150degrees to 60degrees. This is with the expansion tank NOT in the system, Just the boiler. I have shut off the boiler with the shut valves on the return, and on the supply side, before it links into the expansion tank. So I have isolated the expansion tank from the equation.

I am presuming that the water glycol mix expands and contracts based on temperature. So with a 90 degree drop, does it make sense that the pressure within the boiler can go to 0?

Does anyone have a formula to detemrine pressure in a "sealed" vessel based on temperature change?

Regards.
 
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Old 06-30-08, 03:03 PM
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Reason for not removing the well all the way was, I figured you would like to keep as much glycol in the boiler as possible, and to remove the well you, will need to drain the boiler below the well line.

You should not even test the boiler without the expansion tank as you run the risk of letting the relief valve blow off.

And your pressure should START at around 12-15psi when cold then go up from there. It should only go up about 5psi if working correctly. Relief valve will blow at 30psi

There should not normally be a 14psi difference in pressure.
Either your tank is too small or under pressurized.
 
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Old 06-30-08, 05:56 PM
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Jim, I don't know if there's a 'formula' per se, and I believe you would need to start off knowing the volume of water in the isolated section of the boiler...

Straight water will expand in volume approximately 4% with a temperature change from nominal room temp to 180F. I don't know how much a glycol mix will change that percentage.

It is entirely possible that that amount of change in volume will cause what you are seeing. Take a plastic liter soda bottle, fill it with hot hot water, cap it tightly, and let it cool... you'll quickly see what's happening in your boiler !

Mark, in Jim's last post, he said he had the boiler valved off from the expansion tank ... and that it's shut down. But yeah, don't attempt to run it that way !
 
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