Replacing expansion vessel on my sealed heating system

3 Mar 2010
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United Kingdom
Woke up this morning to find water venting out of my expansion vessel (zilmet 18 litre). I managed to isolate the water to the vessel and the leak has disappeared. I removed the pressure from the top of the vessel and unscrewed it from directly above the hot water tank. I have now purchased a cimm 18 litre replacement pre pressured to 1.5 Bar. Is it a simple task of just screwing it back into the housing left by the old vessel or do I have to do anything else? I notice a black rubber cork on the inside the screw do this have to be removed or will the pressure of the water do it once it has been fitted?

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It needs to the correct type, normally orange for heating and white for hot water.

The air precharge pressure needs to be set for the application before its fitted. Typically 0.9 Bar for heating that is to run at 1.5 Bar cold.

I think the "cork" you refer to is probably the bottom of the internal diaphragm, remove that and you will muller your new vessel, just because it is pre-charged dosn't mean that you do not need to check the pressure, for an average 2 storey house this needs to be no more than 1.oobar ;)
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