# What is the correct PSI



## Booter (29 Nov 2009)

How do you know what the correct PSI setting should be for water in a heating system? I have mine between 1.5 & 2 bar, but not really sure where I got this from? Is there a single correct setting? If not, what does is depend on?


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## gary71 (29 Nov 2009)

Anything Below 0.9 bar the boiler can lock out, anything over 2.5 bar you're getting to close to the magic number of 3 bar where the safety valve is fully opened and emptying your system water to outside (hopefully), i set the pressure to 1.5 bar but 2 bar wouldn't worry me, Gary.


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## Booter (30 Nov 2009)

Thanks Gary. 



gary71 said:


> Anything over 2.5 bar you're getting to close to the magic number of 3 bar where the safety valve is fully opened and emptying your system water to outside (hopefully),



We have an expansion tank in the attic which I think takes the place of the "emptying outside" function.  As a by-the-way, when you say "hopefully", what would happen if the system water could not empty outside or into an expansion tank - would the pipes burst?


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## Blake (30 Nov 2009)

I have the original sticker on my Baxi Boiler. It says normal operating pressure is between 1.5 to 2.5 . Anything outside this it says to contact an service engineer. Hope this helps.

Blake


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## gary71 (30 Nov 2009)

Indiansign said:


> We have an expansion tank in the attic


Setting the pressure in a heating system is only a issue for a sealed system filled from the mains by a filling loop, if you have a tank fed boiler then the tank will replenish any water lost and the reading on the guage will only show the effect of gravity on the water and then as it heats up it may show movement on the guage. 



Indiansign said:


> which I think takes the place of the "emptying outside" function.?


 most gas boilers are designed to be used on pressurized sealed systems and mains water fed, because of this most gas boilers come with a 3 bar safety valve fitted inside them, if there is to much pressure building up in the boiler this valve will open and release heating water stopping any further increase in pressure in the boiler, these valves should be plumbed to a safe place.




Indiansign said:


> As a by-the-way, when you say "hopefully", what would happen if the system water could not empty outside or into an expansion tank - would the pipes burst?


 If a 3 bar safety valve is not plumbed to a safe place ie... to outside , then when the valve opens it will empty under the boiler flooding any area the boiler is in, this would be a bigger concern if the water was at i high temperature and someone got burnt, Gary.


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## DavyJones (30 Nov 2009)

gary71 said:


> If a 3 bar safety valve is not plumbed to a safe place ie... to outside , then when the valve opens it will empty under the boiler flooding any area the boiler is in, this would be a bigger concern if the water was at i high temperature and someone got burnt, Gary.




just to follow on from Gary's sound advice, My pet hate is safety valve outlets. Countless times I have seen them terminated out of building at head height, so If they do go and your unlucky enough to be walking by, you get a face of very hot water. the hard work was done by drilling hole out, why can't they be run toward the ground and at a lower position?


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## Booter (30 Nov 2009)

gary71 said:


> Setting the pressure in a heating system is only a issue for a sealed system filled from the mains by a filling loop, if you have a tank fed boiler then the tank will replenish any water lost and the reading on the guage will only show the effect of gravity on the water and then as it heats up it may show movement on the guage.
> 
> most gas boilers are designed to be used on pressurized sealed systems and mains water fed, because of this most gas boilers come with a 3 bar safety valve fitted inside them, if there is to much pressure building up in the boiler this valve will open and release heating water stopping any further increase in pressure in the boiler, these valves should be plumbed to a safe place.



Ours is a sealed system alright - Oil boiler, not Gas. The reading on the guage does increase as the water heats - in fact its at Zero when its cold - I thought this was normal behaviour? Not sure what exactly what a filling loop is, but when I need to increase the pressure (about once a year) there is a little tap head on a pipe leading down from the attic that I open and let in some water.


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## gary71 (30 Nov 2009)

A filling loop is a device that has been specially designed to connects a heating system to the mains water, it has been designed like this to meet the water regs covering this a connection(). It wouldn't hurt for you to have someone identify to you you're safety valve, so you can see where the water is going to go if it ever opens, Gary.




DavyJones said:


> My pet hate is safety valve outlets. Countless times I have seen them terminated out of building at head height, so If they do go and your unlucky enough to be walking by, you get a face of very hot water. the hard work was done by drilling hole out, why can't they be run toward the ground and at a lower position?


Unfortunately i have the answer to that, it's because they don't want the walls stained from contaminated water when the safty valve leaks, Gary.


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