How do I drain hotwater tank in an unvented system?

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I need to change a faulty thermostatic shower valve, and surprise surprise there are no inline isolating valves on it!

How do I drain the hot water side of the system so I can change this part?

I presume the cold water can be isolated just by turning the stop cock off? :oops:
 
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Bas

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The cold can be isolated at the stopcock and the hot tank should have an isolating valve on the incoming feed (to the bottom of the tank). pressure will then stop hot water coming out of the tank. Its a good idea to open a few taps as well to allow some water in the pipes to escape safely. It wouldn't be a bad idea to fit an isolating valve on the new shower.

Hope that helps.
 
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"How do I drain hotwater tank in an unvented system?"
Answer - you don't have to to do what you want!

What might be fooling you, if you have a Megaflo type store, is that there's a big air ppocket in the top which the water compresses. So after you've turned off the supply as Bas says, and turned on a hw tap it takes 10 mins or so to let the squashed air push the water out until the pressure is zero. With the external-pressure-vessel type, it stops much quicker.
 
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