How do I drain my central heating system down correctly?

[spiceman]

Please help again.

I've never drained a system down before so hoped you could tell me how.
I know I have 2 tanks in my loft, 1 small,1 large.
Also I have found which I think is a drain point oustside my house.

Thank you.

 

[Burnerman]

To drain the CH:
Stop water entering the smaller of the loft tanks.
Open any drain down cocks that you can find on the system. Ideally there will be one at the lowest point (but there rarely is!). Dont forget any drains on the boiler.
There will always be some water left in the system though.
John

 

[spiceman]

Thanks John.
I need to replace a 3 port valve that feeds my heating and hot water.
Does that mean I have to drain my HW also.??

Do I open any vents on my rads to allow air in?

Thanks

 

[Hugh Jaleak]

You dont need to worry about the cylinder contents, this water is entirely seperate from the heating side. The hot water from the boiler passes through a coil of copper pipe inside the cylinder, transferring the heat from the primary water (from boiler) into the secondary water in the cylinder, (for the hot taps).

If the 3way valve is at 1st floor level you may get away with lowering the level of the system contents to just below the valve position, no need to drain downstairs rads. Opening rad vents will let air in to assist the drain down. Close again, when drained. Fit new valve, then refill system. Open rads, (lowest first) to bleed the air when filled. I always run system with boiler off for a while to let any trapped air work its way out the vent.

 

[chudsy]

To drain the CH:
Stop water entering the smaller of the loft tanks.
Open any drain down cocks that you can find on the system. Ideally there will be one at the lowest point (but there rarely is!). Dont forget any drains on the boiler.
There will always be some water left in the system though.
John

Hi John,
I'm due to drain and clean my system. I believe there is a drain valve on the side of the boiler as well as all the downstairs rads. Should I drain off from the boiler also?
Cheers
Paul.