Water heater
Posted by Chris on October 22, 2002 at 07:16:30:
About a week ago the electric immersion heater in my HW cylinder died. I replaced a blown breaker (cartridge fuse) and that blew out straight away, with a flash from the head of the heater itself so I guess that's . Years ago I'd have tried to revive the unit, but it looked a little too corroded so I decided not to mess with it and purchased a new heater and thermostat to match.

Let me explain the layout, the immersion heater fits into a vertically arranged cylinder-complex about a meter high with an integral header tank on top of it. The penetration gland is radially oriented close to the bottom of the cylinder so the heater lies across its width and the water has to be drained before its removal.

Now, this is where the problems started. I was not convinced that the stop-cock is completely cutting off the cold water supply from the street. I think it may be defective because as hard as I turn it still hisses when I turn on the faucets, which never run dry. How I attempted to overcome this (I'm reluctant to shut off the water to the whole appartment block) was to turn all the taps hard-on and hope that, being on one level the low pressure differential was enough to prevent the header cistern from filling. Then by draining off the 'hot' water, I reackoned it should have been okay to proceed.

The hot water eventually did stop, but I wasn't able to make certain the cylinder was empty so that's as much progress as I made. One thing I did notice after I'd allowed all the reservoirs to fill up again was that there's no longer any output from any of the hot faucets. It's not a problem yet since the hot water's still not being heated. I guess that's just caused by air in the pipes which I'll have to find some way of bleeding off when I finish the job.

Has anybody any ideas about this? I see it as two problems that have to be addressed separately. In the first instance is this method of shutting off the water sound? And secondly what's the best way to free the pipes of airlocks? I think I know the answer to the latter, the water's drawn from the top of cylinder so if my theory of input pressure being neutrilized is correct, then I should be able to run off the water from the valve near to the bottom. Then if I fill it up with all the outlets turned slightly on I'm hoping it will force any air out of the tubes.

I'm really open to any ideas on this.

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