I'm going to add an extra radiator to my central heating system and will need to drain and refill the system. I have a SIME combination boiler. Is there anything I need to be aware of when draining the system or is it just a matter of shutting off the supply to the boiler and opening the drain (fitted at the lowest point in the system). I'm a bit concerned about creating a vacuum in the boiler expansion tank and damaging it while emptying the system.
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Draining Combi Central Heating System
- Thread starter JJA66UK
- Start date
you don't need to shut off the water
switch off the boiler tho
ex vessel will be ok
make sure the auto air vent is open on the boiler
turn off ALL the rad valves and it will drain quicker as the water will stay in the rads
make sure the cap is loose 
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