Comments on: My central heating boiler seems to boil over with steam emitting into the overflow, what is the problem? http://www.boilershq.com/central-boiler/my-central-heating-boiler-seems-to-boil-over-with-steam-emitting-into-the-overflow-what-is-the-problem All About Boilers Sun, 18 Apr 2010 16:59:59 -0500 http://wordpress.org/?v=2.8.4 hourly 1 By: KrudKutter http://www.boilershq.com/central-boiler/my-central-heating-boiler-seems-to-boil-over-with-steam-emitting-into-the-overflow-what-is-the-problem/comment-page-1#comment-1996 KrudKutter Mon, 22 Feb 2010 21:25:59 +0000 http://www.boilershq.com/central-boiler/my-central-heating-boiler-seems-to-boil-over-with-steam-emitting-into-the-overflow-what-is-the-problem#comment-1996 Dangerous situation - you need to get this looked at. If that valve wasn't there, the system could cook out of control, develop very high internal pressure, and eventually something could literally explode from the pressure. You don't say if you have a steam boiler or hot-water system - same situation, but they operate at different pressures and temperatures. The pop-off valve you're talking about is designed to open when either or both of the following occurs - the pressure is too high, or the water temperature is too high. They do get weak and start to fail prematurely, but in my experience if they're leaking 9 times out of 10 something else is happening. Here are some things to check 1) Water volume in the system. This should be controlled by an automatic fill valve, and really should not change under normal operation. The auto-fill valve could be improperly set, or could be failing, OR, there could be a leak somewhere in the system that is always letting in new (street) water. Look for hidden leaks and drips. 2) Pressure or overflow tank waterlogged : Water expands when it gets hot. No doubt you have some kind of a tank on the system designed to take up that expansion space. If it's full of water or not working, instead of the water expanding, it will build higher pressure in the system (and pop the pop-off valve). This is dangerous - have it cheched. 3) Upper limit controls are not set correctly or are malfunctioning: There should be a high temperature limit switch that shuts off the main burner when the water temp gets to 180 (or whatever it's set for). If this control fails there is nothing to limit the boiler from firing except the room thermostat. It can run-away and start making steam - very dangerous in a hot water system. Usually - once the auto pop-off valve starts to leak, for whatever reason, it should be replaced even if it is not the cause of the problem. It's rare that they'll go back and shut properly if they've been leaking for any length of time. Over-firing boilers are the cause of explosions, fires, basements full of water -- all kinds of bad things. You need to get it checked out ASAP Also - if it is not already - that valve should be piped to within 4" of the floor. Lots of plumbers leave that drop pipe off which makes for a very dangerous situation .If the boiler were to run away, you'd have live steam coming out of that valve, which can cause 3rd degree burns, or worse. The drop pipe at least takes it to the floor instead of at eye level. Good luck<br><b>References : </b><br>Done a lot of HVAC work Dangerous situation – you need to get this looked at. If that valve wasn’t there, the system could cook out of control, develop very high internal pressure, and eventually something could literally explode from the pressure. You don’t say if you have a steam boiler or hot-water system – same situation, but they operate at different pressures and temperatures.

The pop-off valve you’re talking about is designed to open when either or both of the following occurs – the pressure is too high, or the water temperature is too high. They do get weak and start to fail prematurely, but in my experience if they’re leaking 9 times out of 10 something else is happening. Here are some things to check

1) Water volume in the system. This should be controlled by an automatic fill valve, and really should not change under normal operation. The auto-fill valve could be improperly set, or could be failing, OR, there could be a leak somewhere in the system that is always letting in new (street) water. Look for hidden leaks and drips.

2) Pressure or overflow tank waterlogged : Water expands when it gets hot. No doubt you have some kind of a tank on the system designed to take up that expansion space. If it’s full of water or not working, instead of the water expanding, it will build higher pressure in the system (and pop the pop-off valve). This is dangerous – have it cheched.

3) Upper limit controls are not set correctly or are malfunctioning: There should be a high temperature limit switch that shuts off the main burner when the water temp gets to 180 (or whatever it’s set for). If this control fails there is nothing to limit the boiler from firing except the room thermostat. It can run-away and start making steam – very dangerous in a hot water system.

Usually – once the auto pop-off valve starts to leak, for whatever reason, it should be replaced even if it is not the cause of the problem. It’s rare that they’ll go back and shut properly if they’ve been leaking for any length of time.

Over-firing boilers are the cause of explosions, fires, basements full of water — all kinds of bad things. You need to get it checked out ASAP Also – if it is not already – that valve should be piped to within 4" of the floor. Lots of plumbers leave that drop pipe off which makes for a very dangerous situation .If the boiler were to run away, you’d have live steam coming out of that valve, which can cause 3rd degree burns, or worse. The drop pipe at least takes it to the floor instead of at eye level.

Good luck
References :
Done a lot of HVAC work

]]> By: keith p http://www.boilershq.com/central-boiler/my-central-heating-boiler-seems-to-boil-over-with-steam-emitting-into-the-overflow-what-is-the-problem/comment-page-1#comment-1995 keith p Mon, 22 Feb 2010 20:49:59 +0000 http://www.boilershq.com/central-boiler/my-central-heating-boiler-seems-to-boil-over-with-steam-emitting-into-the-overflow-what-is-the-problem#comment-1995 One it is not removing the oxygen from the water 2 your overflow is not a pressure relife valve it is your thermastst in your central heating boiler what is on its way out .<br><b>References : </b><br> One it is not removing the oxygen from the water 2 your overflow is not a pressure relife valve it is your thermastst in your central heating boiler what is on its way out .
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]]> By: Turdy malurdy http://www.boilershq.com/central-boiler/my-central-heating-boiler-seems-to-boil-over-with-steam-emitting-into-the-overflow-what-is-the-problem/comment-page-1#comment-1994 Turdy malurdy Mon, 22 Feb 2010 20:21:59 +0000 http://www.boilershq.com/central-boiler/my-central-heating-boiler-seems-to-boil-over-with-steam-emitting-into-the-overflow-what-is-the-problem#comment-1994 The thermostat control on the boiler would appear to be at fault and needs replaced.<br><b>References : </b><br> The thermostat control on the boiler would appear to be at fault and needs replaced.
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]]> By: Fraz http://www.boilershq.com/central-boiler/my-central-heating-boiler-seems-to-boil-over-with-steam-emitting-into-the-overflow-what-is-the-problem/comment-page-1#comment-1993 Fraz Mon, 22 Feb 2010 20:14:59 +0000 http://www.boilershq.com/central-boiler/my-central-heating-boiler-seems-to-boil-over-with-steam-emitting-into-the-overflow-what-is-the-problem#comment-1993 It appears to be overheating, the overflow is a pressure relief valve and suppose to open and release the extra pressure/steam/water if the boiler heats the water too much (a hot water heater will do the same too), it prevents them both from exploding from too much pressure. On the boiler there should be a guage showing the temperature/pressure of the water/steam, it will also have a red line point that indicates the maximum temperature/pressure and it should not cross that red line. If the temperature/pressure is below the red line and normal then it's probably a malfunctioning/bad pressure relief valve, they do wear out over time and need replacing. Switching it off allows it to cool down as well as release the extra pressure until the relief valve closes again.<br><b>References : </b><br> It appears to be overheating, the overflow is a pressure relief valve and suppose to open and release the extra pressure/steam/water if the boiler heats the water too much (a hot water heater will do the same too), it prevents them both from exploding from too much pressure. On the boiler there should be a guage showing the temperature/pressure of the water/steam, it will also have a red line point that indicates the maximum temperature/pressure and it should not cross that red line. If the temperature/pressure is below the red line and normal then it’s probably a malfunctioning/bad pressure relief valve, they do wear out over time and need replacing. Switching it off allows it to cool down as well as release the extra pressure until the relief valve closes again.
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