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Hot water conundrum

RogerS

RogerS

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I want to drain down the hot water tank which is the traditional vented design. Feed from the cold water tank at the bottom and pipe out of the top with a vented pipe going up into the loft. There is a gate valve in the feed from the cold water tank.

Turning this off certainly stops the water flow from the HW taps but I would have expected a lot more water while the HW tank drained. But it doesn't. Turn off the gate valve and immediately the hot water taps stop. The only reason that I can think of is if the vent pipe is blocked but find that very hard to comprehend how it could happen (if it has).

Confused am I.
 
Roger,

Once you have shut the gate valve there is no pressure to push the water out the top of the tank. Hopefully there is a drain cock fitted to the cold feed to the tank, between the tank and the gate valve, thats what you should use to drain the tank.
 
Doh! :eusa-doh: :eusa-doh:

How obvious....to anyone else but this numpty! Thanks Dave...will look tomorrow.
 
And if the drain cock doesn't exist or is seized the only way to empty it I can think of is to remove the hot connection at the top and syphon the water out. Guess a garden hose could help there.
 
Whilst we're on the vagaries of vented HW systems, I once had a house where a steady stream of water started to come from the heating and HW header tank overflow. I turned off the mains feed to the header tank, and the water carried on flowing. I had discovered perpetual motion, or so I thought. After a lot of head scratching it turned out that there was a a breakdown in the secondary heating coil inside the HW tank. Although the heating header tank had been isolated, water from the primary feed header tank was mixing with the secondary feed and flowing up into the heating (secondary) header tank and out of the overflow.

Having worked out what was going on, and being completely skint at the time, I was able to get to B&Q just in time to buy a new HW tank, some pipe and fittings, and spent until 3am the next morning replacing the tank myself. The joys of home ownership!

In this case, draing the HW tank was not a problem, as it was mixing with the secondary circuit so I was able to drain it through the CH heating drain cock! :lol:
 
Can't get my head round that one, Roger. If you turned off the mains then how did the water rise up? :eusa-think:

Luckily I do have a drain cock.
 
Both primary and secondary tanks had their own mains feed, after the stopcock for the entry of water to our house. I turned off the secondary system feed which should have stopped the overflow from the secondary header tank. But it kept on flowing. What was really confusing was that when I turned off the main stopcock into the house, water still carried on flowing out the secondary overflow for quite a long time.

It turned out that the primary domestic header tank was higher than the secondary, so even with the mains turned off to everything, there was still a head of water from the primary that could flow down into the DHW tank and back up the feed from the secondary header tank and out the overflow until the water levels had equalised. I thought I was going mad! :lol:

With the main stopcock on, and the secondary tank (supposedly) isolated, water just flowed indefinitely, as it still had a mains feed to the primary tank which then mixed with the secondary inside the DHW tank through the failed secondary coil and flowed back up the feed pipe into the secondary header and out the overflow from a header tank that I thought had been isolated!!!! Aaaaaggghhh :twisted:
 
LOL... I know what you mean. I turned off the feed to our HW tank as per the OP and ran the hot tap downstairs to empty the tank. Of course, I now realise that I would not empty the tank. However what is still perplexing is that NO water came out and I would have thought that the residual water in the pipes from the top of the HW tank down to the ground floor would flow...the pipe being vented by the vent pipe. But nowt.

Mind you, I do get it right sometimes. Last time I was at the windsurfing hotel, woke up to find the hotel had no water ergo no hot morning shower. Then I remembered the showers in the basement ..."Not a lot of people know that" I thought. So I trundled down there and found enough hot water in the pipes in both gents and ladies showers (shy, moi?) to have a refreshing shower. Up to breakfast to hear people grumbling about not being able to shower :twisted: [/smug mode]
 
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