Sealed systems have an expansion vessel that absorbs the pressure as the water in the system expands due to the heat in the system. Whereas open vented systems have an expansion pipe that lets out the pressure. Open vented systems are more prone to rust in the system.
Over time this will reduce the effectiveness of the radiators and the boiler will need repairing. Chemicals can be added to the system to reduce this. However sealed systems are more efficient.
Sealed systems pros
- Less rusting
- Less likely to suck air in to the system creating air locks and rust
- If a radiator is damaged, only half a bucket of water will leak from the system.
Sealed system cons
- When the pressure reduces the boiled will stop working. (Regular servicing is needed)
- A pipe must lead to outside for the pressure relief valve to dump the excess pressure when problems occur with the boiler
Open vented system pros
- If the system is very old and has lots of small leaks the pressure will never stop the boiler from working
- If the system is very old no excess pressure will be put on pipes and radiators creating leaks.
Open vented system cons
- Less efficient
- More rust in system
- More space is taken up from the tank.
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