Motorised valve replacement - Must I drain down whole system

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I need to replace my sticking HW m/v, shown on the attached picture. How do I stop water spurting out as I do it ? Artic Freeze would not work for me - do I have to drain the whole CH system and empty the HW cylinder or is there an easier way ?


http://s630.photobucket.com/albums/...tion=view&current=Boilercupboard.jpg&newest=1



headache5678_photos


Cheers,
 
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Looking at the pic. I would say that if you live in a single storey dwelling, yes you just about have to drain completely.
If you live in a 2storey and the valves are on the upper, just drain down to below the valves. using a dish/bucket and testing with opening connections occasionally
 
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Thank you - I live in a 2 storey house and this boiler cupboard is upstairs. May I clarify - :

(1) Will I need to (mostly) drain down both the HW and CH parts of the system. Previously I emptied the HW cylinder and jammed the loft tank valve closed but water still poured out into my waiting bowl.

(2) In normal usage, and when I drain down, should the gate valve with the red handle be closed or open in both cases ?
 
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I am sorry to be thick here but it is the HW m/v I need to change (maybe I was unclear) -

- so is it really the CH that I need to drain down ?
 
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You need to drain the primary system, i.e. the water in the boiler and radiators, this also circulates through the cylinder to heat the hot water. (The two do not mix, the water that comes from the hot taps is heated by the water in the primary circuit.)

The secondary side i.e. cylinder and hot supply to taps is independant of the primary circuit so no need to drain this to replace the M/V.
 
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Excellent advice chaps. It all went well once I drained the CH system.

Mucho gracias
 

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