How to Drain immersion tank?

jace_da_face

My hot water tank needs an immersion element replaced. I went and bought a replacement but when it came to replacing it I realised I have no way of emptying the tank. ???

The cylinder is for domestic hot water only. I don't have central heating running from it. So there is a cold water supply feeding the bottom of the cyclinder and hot water pipe exiting from the top to supply taps. Isolating the cold water feed is straight forward. The problem is, I can not see how this tank can be drained. There is no drain cock on the supply pipe.

I did isolate the feed to the tank and run a hot tap. As I suspected, running the taps was never going drain the tank. The tap ran for about a minute before running out.

If there is no drain cock on the supply pipe then all I can think of doing is to somehow remove the pipe at the top and ciphen the tank.

Any suggestions?

FoxT

when you drain the water out of the tank, you have to have a way of letting air in. Otherwise, as you have discovered, the water simply wont flow out.

Some options you have are:

OPTION 1:Assuming the following:
2 storey house, cold water feed is a gravity feed from a header tank.

If this is the case, tie off the ball cock on the header tank so that when you turn on the taps the header tank will not refill as the water level drops. Turn on as many HW taps as you can, downstairs, and you will siphon out all the water from the HW tank


OPTION 2:
shut off the cold water feed. Turn on HW taps, and leave them fully on.
slowly disconnect the HW pipe from the top of the tank, very little water will come out as the taps will drain it away as air is permitted to enter.
Remove the pipe fully then siphon off 3-4 bucketfuls of water with a length of garden hose. As the element is near the top of the tank you wont have to drain it completely

jace_da_face

Your assumption is correct FoxT. It is a 2 story house with a gravity feed from attic tank. I see your point regarding the need for replacing evacuated water with air. As I was only shutting off the valve that feeds the tank then I was not allowing air in via the supply line.

I still don't think that option 1 will work for me for the simple fact that the HW pipe connected to the top of the tank is not fully immersed in the tank. So it will not siphon through the taps. Not beyond a certain point anyway.

I should point out that it is a double immersion system and naturally the heater I need to replace is the one near the bottom. So I will have to drain most of the tank.

Option 2 looks like the way to go I think but I will have to pretty much drain the whole tank.

Thanks mate

FoxT

hmmmm... yes, at some point (fairly early in the proceedings...) option 1 will fail. Had forgotten about that, duh. Option 2 should work though.


As you have the system drained, you could consider installing a drain valve on the CW feed pipe. Might be handy if you get into trouble with it again.

and finally, if your immersion element is of the screw-in type, it is worthwhile to loosen it just a little BEFORE you drain the tank. reason: the tank walls are very thin & if the threads are seized you could damage the tank. This is less likely to happen when it is full of water, as the walls will be more rigid. Also, when pressurised the tank expands a little so the threads sould open a little easier.

jace_da_face

That sounds like very good advice.

Cheers!