Gs boiler blowing steam through relief valve


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Old 01-20-09, 11:05 AM
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Gas boiler blowing steam through relief valve

My gas boiler is a hot water system.It was blowing steam and water from the temperature relief valve. We changed the relief valve, and expansion tank. It still blew . Last year we changed the aquastat relay. My plumber thinks the relay is bad...and not recgonizing the boiler temp... and therefore creating steam, causing it to percolate and blow. Is this true. Is a hot water system supposed to make steam ???
 
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Old 01-20-09, 11:20 AM
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I hope you have a pressure and temperature gauge on your system. What do they read?
 
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Old 01-20-09, 11:25 AM
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the guage on top read read 180 when the steam was blowing, i could not read the other number
 
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Old 01-20-09, 11:52 AM
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Well, you shouldn't be getting steam with a 180 degree temperature level. You can read the settings for the relief valve on the metal tag attached to it.

I'm supposing that it's a pressure and temperature relief valve that's opening, and that it may be opening because of too high pressure. At what temperature and pressure does the tag say the relief valve should open?
 
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Old 01-20-09, 12:16 PM
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I miss read the guage...the temp was close to 240 degrees or more when the valve was discharging. The tag reads 30psi...no temperature info ... it says 510 BTU/HR.
 
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Old 01-20-09, 12:42 PM
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Do you know which aquastat controls the boiler temperature? It's not uncommon for there to be several aquastats doing different things on a boiler system.

I'm presuming this is set up as a hydronic heating (hot water) system, and not as a steam system. If that's the case, 240 degrees is clearly too hot.

An aquastat temperature for a hydronic heating system could be set for temperatues ranging from 140-200 dgrees. What setting is on the aquastat?


What was the reason given for changin out the relief valve and expansion tank? Guessing as to what the problem might be is not the mark of a good repairman. Knowing how to test for possible defects and eliminate them until you identify the actual problem is the right approach.

That said, if you have 240 degree temperature and the operating aquastat is set for someplace in the 140-200 degree range, there is a problem if you are checking the right aquastat.

How many aquastats do you have on your system and what do they do?
 
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Old 01-20-09, 01:09 PM
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Does the pressure relief valve blow off quickly when the system is cool or does it take a long time to blow off. If it blows off fast then the boiler may not be full of water. If it blows off after a long time then there could be a control problem. What is your aquastat set for? Did you try turning down the dial on it while it is running to see if the control is sticking keeping the gas valve energized? An average temp. setting is 180degrees. If you are getting 240 degrees then that is way too hot. I would try letting the system cool down, then check the pressure gauge and see that it shows app. 12 psi. Then start up the system and see how long it takes for the pressure and temperature to rise causing the relief valve to open. The normal operating pressure is between 12 and 22psi.
 
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Old 01-20-09, 01:22 PM
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Unfortunately for me , I'm not sure of the repairmans thinking. There is 1 aquastat on the boiler. It is a hydronic (hot water system) The aquastat temp. was set at approx. 170 degrees, and it was blowing steam .
 
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Old 01-20-09, 01:27 PM
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Well the aquastat should be shutting off the boiler at 170 degrees.

Prudence suggests leaving the boiler turned off until it's been inspected and repaired. It certainly sounds like the aquastat is bad.
 
 

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