Boiler releasing water thru relief valve

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  #1  
Old 09-09-05, 09:58 AM
bitpicker1011
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Boiler releasing water thru relief valve

I searched but didn't find this problem.

I bled the all of air from the system (I think) and charged the blatter expansion tank with 12psi as printed on the tank. The system has an auto feed valve set at 15psi. Once it fires my boiler pressure grows to 30psi and the relief valve discharges water (as it should). I know the expansion tank blatter isn't leaking because I removed the valve from the bottom of the tank and no water was present. My system is about 17 years old and I have never had this problem before. I actually replaced the relief valve when this started happening before I looked at the gauge on the boiler and realized the old relief valve was working properly.

What will cause the excessive pressure? Can expansion tanks fail to do their job over time?

Thanks in advance for your comments.
 
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  #2  
Old 09-09-05, 05:31 PM
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Overpressure

A possibility is the auto feed valve is leaking thru. The easiest way to check is to get the boiler up to 12-15 psig & turn off the valve up or downstream of the feed valve. Does the boiler also make your domestic hot water with a tankless coil?
 
  #3  
Old 09-12-05, 08:20 AM
bitpicker1011
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Originally Posted by Grady
Does the boiler also make your domestic hot water with a tankless coil?
I don't have tankless coil for my domestic hot water. I have a storage tank with heat a exchanger inside which is simply a third zone off my boiler.

Originally Posted by Grady
A possibility is the auto feed valve is leaking thru. The easiest way to check is to get the boiler up to 12-15 psig & turn off the valve up or downstream of the feed valve.
Last June while troubleshooting this problem I did close the shut off before the auto feed valve and it seemed to stop the problem. But shouldn't that valve be open allowing water to enter the system when needed? I was afraid to keep it closed thinking it was put there for a reason other than the initial fill. The auto feed appears to be simply a one way valve and a pressure regulating valve set to 15 psi connecting a domestic water line to the boiler return. I assume it only will feed water to the system whenever the pressure in the boiler drops below 15 psi. True?

I'm fairly technical but I'm not trained in plumbing and heating so please bear with me if I mix up terms.
 
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Old 09-12-05, 06:47 PM
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Auto fill valve

In theory, you are correct. However, this is a mechanical device & is subject to failure in various ways. Instead of an auto fill valve, I much prefer a manual valve & a low water cut-off which will shut the boiler down if the water level gets too low. Auto fill valves are very common & work well, when they work. If shutting off the water to the fill valve stops the discharge, it is almost certain, the auto fill valve is failing to shut all the way.

If when you shut the valve to the auto fill vavle, you are also shutting off the domestic, the problem could be in the domestic coil, if the boiler is so equipped. Hopefully, there is also a manual valve between the auto fill valve & the boiler. If there is, this is the valve to close for testing purposes.
 
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Old 09-13-05, 10:09 AM
bitpicker1011
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Originally Posted by Grady
If shutting off the water to the fill valve stops the discharge, it is almost certain, the auto fill valve is failing to shut all the way.
I've lost a bit of the theory here. Does the auto fill valve actully close? I thought it's purpose was to constantly apply 15psi to the closed system allowing water to enter only when the pressure falls below that. In other words I though with this type of setup the pressure in the boiler will never drop below 15 psi.

Originally Posted by Grady
Instead of an auto fill valve, I much prefer a manual valve & a low water cut-off which will shut the boiler down if the water level gets too low.
I know in a steam system there is a "water level" to be maintained but I thought in a closed hot water system the boiler, baseboard units and all piping should always be full of water.

Originally Posted by Grady
If when you shut the valve to the auto fill vavle, you are also shutting off the domestic, the problem could be in the domestic coil, if the boiler is so equipped.
No there is an isolated shutoff that controls the water feed to the boiler only. Is it OK to close that and keep it closed?
 
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Old 09-13-05, 08:11 PM
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Bitpicker

You actually have a better grasp of the theory than many in the trade. The auto fill valve, properly known as a pressure reducing valve, (hope you don't mind the lesson in terminology) only feeds water when the discharge side of the valve senses pressure less than that at which the valve is set for. This being the case, no water flow, when the pressure is at or above the set point, the valve is "closed".

Your statement about the steam & water systems are absolutely correct. If pressure or water level were to drop on a hot water system the usual call would be for no heat. Only if the piping were to go below the boiler (such as with the boiler on the living floor & piping going down into a crawl space & back up) could one not have heat if the boiler got dangerously low on water. Another instance could be in the summer when the boiler is only used for domestic. The boiler or piping could develop a leak causing a loss of water.

Without a low water cut-off, I would not suggest keeping the valve closed. Close it only for testing purposes & keep a close eye on the pressure until you are comfortable there is no loss in pressure. After you are sure there is no pressure loss, check it in 1,2,4,8,24,& 48hrs. If you see no change in pressure in that time, you can be pretty sure the pressure increase is due to the reducing valve steady feeding.
 
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Old 09-14-05, 08:29 AM
bitpicker1011
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Originally Posted by Grady
(hope you don't mind the lesson in terminology)
Absolutely not. It's exactly what I'm looking for.
Originally Posted by Grady
Without a low water cut-off, I would not suggest keeping the valve closed. Close it only for testing purposes & keep a close eye on the pressure until you are comfortable there is no loss in pressure. After you are sure there is no pressure loss, check it in 1,2,4,8,24,& 48hrs. If you see no change in pressure in that time, you can be pretty sure the pressure increase is due to the reducing valve steady feeding.
Actually, I had shut off the pressure reducing valve when this problem first surfaced and I saw no loss of pressure. But there was also no excess pressure either (the relief valve didn't discharge water anymore). I will do as you suggest but this time I will be careful about recording pressure readings - after the boiler has been on and after it has cooled.

Just so I am clear -
1. This a closed system.
2. With boiler cold and pressure reducing valve on - should have 15psi.
3. Turn off the pressure reducing valve.
4. When the boiler fires the pressure will go up but not as high as 30psi if the blatter expansion tank is doing its job - so no discharge from the relief valve.
5. When the boiler returns to cold the pressure should return to 15psi because nothing left the system and nothing entered.
Sound right?

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  #8  
Old 09-14-05, 03:58 PM
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Bitpicker

You have it. Make sure the air charge on the tank is the same as the pressure for which the reducing valve is set.
 
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