Replacing an immersion heater

[GB]

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.

[Bob Minchin]

You only need to cut off the cold supply from the header tank and drop the water level down to the level of the immersion flange - usually on the top. Cracking a crusty seal can be a swine. Huge leverage on an immersion spanner is NOT the answer but instead short sharp shocks to the spanner usually work.

Usually the fibre sealing washer is quite thick - around 3mm. If it really stuck stubbornly, use a hacksaw blade to cut into the washer sideways all the way round stopping when you hit the immersion collar thread and break the crusty seal that way.

However you do it, scrupulously clean the sealing face on the tank and always use a new sealing washer.

[David]

Not much help directly, but I would be prepared to replace a 40 year old cylinder on general principles because of the risks of something breaking if you do anything.

If a hard water area it is likely to be clagged up anyway, and modern cylinders tend to be better insulated.

I would run the hot water off anyway (perhaps over a period which allows me to use it).

I assume that you have a drain tap at the bottom :-).

Garden hose will cope with hot water (we have used one to fill a water bed from the hot tap).

Ummm....if you have hot water, why do you have to replace the immersion heater?

Or is this the best window of opportunity?

Cheers

Dave R

[GB]

I'll pretty much empty it anyway. The last thing I need is the tank splitting and deluging very hot water.

So, tap the spanner with a hammer?

That sounds good, thanks.

There are two immersion heaters. One is for night time cheap electricity. The one I am replacing is the daytime one.

[Peter Andrews]

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.

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)

[DerbyBorn]

Best to leave it until you have a time when merchants are not going to close. Question for the experts - Is it preferable to try and crack it loose whilst it is full of water - to avoid risk of damage to the cylinder???

[Peter Andrews]

My previous post assumed (wrongly) that you had a single immersion heater at the top! Same applies though just that you will need to siphon out rather more water to avoid spillage when removing the heater.

Peter

[Thomas Prufer]

Something to ease it will not be amiss, as in WD-40, Plusgas, etc.

Cool the tank, because loosening the thing is easier on a full tank, because the water supports the tank and gives it bit of heft. And you don't want hot water spewing everywhere.

It's easy: You will loosen the heater with the tank full just enough so it doesn't leak (much), but comes off easily once the tank is drained.

(Yeah, one of those jobs to approach with a sense of doom.)

Thomas Prufer

[GB]

That's really my question. My concern is that, if it buckles and splits when full of water, that's even more of a disaster!

[Dave Plowman (News)]

Run it out via the taps? It will then be replaced with cold. There may be less risk of damage to the cylinder and pipes if it's full of water - the extra mass will help stop it moving.

[Fredxxx]

I'd prefer to make sure its empty some way under the immersion tank opening. In the past I have worried about the tank giving but being copper it ought to be ductile and if there is any tearing it ought to be around the mounting itself.

If exceptionally tight, I might use a hammer to tap it round rather than apply extreme force with the worry it can all give way before I can remove the force! LOL

[DerbyBorn]

.

Consider using Copaslip or some other thread lubricant when installing - but take care this does not let you overtighten it. The washer needs to be just nipped - not crushed to death.

[DerbyBorn]

Definately light taps.

[Dave W]

In my case, there is a drain c*ck 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.

[Tim+]

40 years? What's the insulation like? If it's a strap on jacket I would just change the cylinder.

Tim

[Nick]

I did this a few weeks ago.

Huge torque will destroy the cylinder, they are relatively soft.

The thing that worked for me was a blow torch, heating around the top where it screwed into the cylinder.

I'm not totally sure why but I think it was because the heat softened the jointing compound that had been used on the thread.

[Nick]

Forgot to say buy this type of spanner

I tried this cheaper one and it was rubbish

[Harry Bloomfield]

It will not suddenly split, it will buckle first giving plenty of warning. Try tapping spanner towards tighten and well as slacken.

Is this a soldered in lug or original fitment?

[GB]

You mean the boss for the immersion heater? It looks like it was originally on the cylinder when made..

[DerbyBorn]

Is an immersion heater one of those situations where - as it is the washer and the faces that perform the function of sealing, it is totally un- necesary to apply any sealant to the threads. (I wouldn't - I would just ensure the faces were free of debris and damage - and the washer was good.)