"Peter Andrews" wrote in message
news
On 28/12/2016 10:27, GB wrote:
I need to replace an immersion heater that's been in the cylinder for
over 40 years. It looks well crusted in place. So, how much force can
you put on it to unscrew it without rupturing the cylinder? Is there
anything I can do to ease it, or is brute force the way to do it?

Also, the cylinder is full of hot water. I'll need to drain the cylinder
through a hose at the bottom. Will an ordinary garden hose be okay with
piping hot water, or do I need to cool the cylinder down first by
running off the hot water?

You can tell that this is not a job I've done before.



Turn the water supply to the cylinder off and turn on the hot taps, they
should stop running in a couple of minutes as the tank will stay full as
the outlet is at the top of the tank. Carefully slacken / undo the
compression fitting above the top of the tank where the hot water pipe
tees (to the taps and the expansion pipe) mopping up any spillage - if
everything is turned off properly a couple of towels should suffice.

Use the correct box spanner (e.g.
http://www.toolstation.com/shop/p80367?table=no) with a bar so that you
can apply turning force to it on both sides at the same time. Just slacken
the heater to break the seal, then insert a hose to siphon out the water
to just below the heater hole and then remove and replace the heater. Do
not attempt to unscrew the heater if the tank is empty it will just
buckle.

It's one of those jobs that I have done two or three times but now days I
have a friend who is a plumber and, for the sake of my nerves, I prefer to
pay him to do it!

I'm sure others will be along with advice as well.

Peter (I am not a plumber)

In my case, there is a drain cock at the bottom of the cylinder, allowing me
to get the water level below that of the immersion mounting prior to
unscrewing.

Once, I did indeed rip the tank trying to unscrew the immersion. I was
amazed at how thin the copper was, so be warned! I soldered copper patches
over the tears as an interim solution.

I would say try to avoid the use of boss white on the new fibre washer, as
that's what hardens and makes removal difficult. PTFE tape round the screw
thread should be OK if it can be done without tearing.
--
Dave W