Converting open vent to sealed system.

15 Apr 2008
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United Kingdom
I have a very badly installed (apparently by a HETAS qualified engineer!) oil fired central heating system. In order to resolve the problem with the vent for the system coming off the return, and travelling most of the way around the house, I would like to convert the system into a sealed non-vented system. Is there any reason why I cannot do this with the current boiler? Is it the case that I simple replace the expansion tank with an expansion vessel, and provide a means of pressurising the system from the mains?
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You'd certainly need to establish that your boiler has a high temperature cut-out and that any system pipe work & fittings can take a higher pressure.
Richard, thank you. THere are some bits of hep that I would remove, otherwise all joints will be copper soldered. THe boiler has a variable thermostat, and clearly i would fit a pressure safety valve. I suppose the question is - most closed system boilers are fitted with an expansion vessel - but providing it can as you say take the pressure, is there any need for the expansion vessel to be integral with the boiler? If not, how close does it have to be - I assume as close to the supply outlet as possible?
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You can fit an expansion vessel externally to the boiler but the first thing you must do is check that your boiler is actually approved for use on a sealed system, as not all of them are

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