Removing old immersion heater

I spent yesterday replacing the immersion heater in our hot water tank. It was not an easy job, but I found this site and others very useful to get ideas about what to do.

The old immersion heater was fitted about 35 years ago when the house was rewired (a few years before we bought it). About a month ago it started making singing noises like a kettle and the heat output dropped. The other day it stopped working altogether.

When I tried to take it out, the thing was totally seized. The tank is quite sturdy, being an old 1950s cylinder with a brazed-in boss at the top. I drained it about 9 inches below the top so most of the water was still in it. The box spanner I bought from B&Q looked quite sturdy, however the bar supplied with it just bent when I used it with a bit of extra leverage.

The old unit looked like it had been fitted with Bosswhite or a similar cement that had gone rock hard. We have soft water, so limescale is not a problem. I used a hacksaw blade to cut through the fibre washer between the heater and the boss - a laborious process. I put in some penetrating oil and left it for a while.

Meanwhile I welded the box spanner to a 2 foot length of 2" angle iron so I could apply a lot more force and also apply some impact with a club hammer. Without this improvised tool I would never have got the old unit out.

It still wouldn't budge even with quite a lot of hammering. Finally I heated the boss with a flame for several minutes. Then I tried knocking it back and forth. Finally I tried turning it again applying quite a lot of torque. You do have to watch how the cylinder is coping.

At last I got a bit of movement and slowly I unscrewed it. The threads and been completely covered with Bosswhite or similar.

To refit the new one, I put PTFE tape round the threads and applied a good bead of blue silicone sealing compound as used in automotive applications to both sides of the gasket. At least If I have to take it out again it should move!

One final point. The mating surface on the boss had been slightly damaged by using the hacksaw blade. I had to carefully file this down to get a smooth surface. Make sure the filing is done evenly round the boss, so the mating surface remains at 90 degrees to the thread.

I hope this is useful to others. I've done a lot of plumbing of all sorts over the years including central heating, bathrooms etc., but this was one of the hardest jobs. In summary, you are going to need quite a big wrench, with a two foot lever. After seeing why the threads were stuck, I don't think the penetrating oil made much difference. Hammering it alone, didn't seem to work. The crucial thing seem to be the heat as the differential expansion probably cracked the cement bond.

Hugh

Reply to
Hugh
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Seems to me that your HW tank must be made of high tensile steel if can stand a spanner with a lump of angle iron thereon;!..

Most copper cylinders already start to buckle when they see the spanner coming;..

especially ones of some age..

Reply to
tony sayer

The message from tony sayer contains these words:

Nah .......... my IH spanner has an 18" piece of angle iron welded to it (and needs it) and I haven't buckled a tank yet with it. Changed our own IH last month -- tank dates from late 1970s .

Reply to
Appin

Thanks for that.It bolsters my confidence to do the same to mine - 82/83.

Reply to
Clot

Yes the "spanner" does sound a bit brutal, but I think the weight is small compared to the force you need to apply. If you have the clearance it might be an idea to weld the box spanner in the middle of the bar so you can push and pull. That way you apply pure torque and minimise the sideways force on the tank

Although the wrench is long, I don't advocate just heaving away on it as something will probably give. From what I saw, it was necessary to try and break the bond with heat and impacts before applying a lot of torque.

On some other threads, I noticed folk questioning the advantage of leaving the tank mostly full if possible. I think there are two advantages. Firstly the tank is very heavy so it's easier to apply force without disturbing the plumbing too much. Secondly, the weight of water will create tension in the walls of the cylinder and make it less likely to buckle. Same idea as a prestressed concrete lintel.

Cheers, Hugh

Reply to
Hugh

"Don't force it, get a bigger hammer", has a lot of truth behind it.

If you apply an adequate force for the job, using over-sized tools that can apply this force once, in the right place, in a controlled manner, then your chance of breaking something is much reduced compared to randomly hammering away at it with something too small and just hoping.

Reply to
Andy Dingley

A few months ago I had six feet of breaker bar on the lower of the two elements for our water heater - I gave up at that point (the element wrenches proved to be the weak point and kept distorting and rounding out with that much force on them).

"thankfully" I just wanted to remove the lower element to get access to the sludge in the bottom of the tank, not because it was faulty. In the end I managed to proggle things out sufficiently with a bit of baling wire through the drain valve body, and a *lot* of flushing. One day that element will fail though, and then it'll be new tank time...

Reply to
Jules

I've never tried removing elements by constant applied force: I always tap at them moderately hard with a hammer until they start to move enough to undo by normal hand on a normal pressed-steel spanner. Sometimes it may take quite a long time for them to start to shift, but I've only had 2 failures: one where the blanking plug I was trying to remove simply refused to budge and the cylinder boss was buckling alarmingly, the other where the boss started to split away from the rest of the cylinder almost as soon as I touched it.

Reply to
YAPH

Sorry that sounds a bit garbled.

I tap on the end of the immersion heater spanner with a hammer, not directly on the fitting. I prefer to use a club hammer and tap fairly gently (certainly nothing like full swing!) rather than hitting harder with a lighter hammer. Eventually it starts to move and when it gets to the point when I can turn it by hand, using the spanner, I do that.

Reply to
YAPH

Which makes me wonder, has anyone tried an impact driver for this job? Achieve loads of taps very quickly and easily. (And I'm sure someone could see how to make it work with an immersion heater box spanner thing.)

Reply to
Rod

No, but they are great for removing old painted in screws in door frames - and they work a treat with screw extractors.

Reply to
The Medway Handyman

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