Help! Advice for replacing blown immersion heater/thermostat?

[Marco]

Hi, Hope someone can help please as this is my first immersion job!

I was caled to a relatives house who wants to use immersion heater only for heating water in summer (located in bedroom). However water was overheating and now immersion has now 'blown'. No massive emergancy as they are happy to use bolier to heat water for now.

On arrival I stripped took off the immersion heater cover, but the cables were burnt out to the thermostat and the insulation on the (1.5mm?) 3 core cable and to supplimentary bonding earth looked pretty heat damaged as well. I've replaced the thermostat and cable, initially to see if it is only that what was damaged, but have not made the final connection as I was a bit worried abou the old surrounding electrics etc.

Here's the first question: I asked a the plumbers merchants for heat resistent 2.5mm 3 core cable, but he reakoned 1.5mm heat resistant is ok, which I've fitted for now - but not connected to switch! Is he right, or should I be replacing with 2.5mm heat resistant?

Secondly, all the books say to use a fused double pole 20amp isolating switch near the tank. Currently there is an old unfused switch near the tank (although in decent condition) used to switch the immersion on and off, there is another fused switch downstairs (fuse currently removed!). As this is a replacement of a broken item, is it ok to wire into the old switch next to the tank? Even if so, presumably it would be better to replace this, but relative is keen to keep price down!?

Finally, I was going to replace the whole immersion at first, however, it is pretty well corroded in at the top, and despite soaking with WD40, it doesn't want to move! I've not given it to much welly as I hear it is very easy to buckle the copper tanks! Hence trying to replace only the thermostat for now. Has anyone got any top tips to remove the immersion element safely please?

Any help gratefully received!

 

[dmholt24]

i would of used 2.5, have you used an immersion spanner on it

 

[helpsy]

Hi
I haven't replaced an immersion yet as new to the trade, but I have noted people saying that you need to initially "crack" the joint with the water still in the cylinder,then when you get some movement drain down and take out immersion.
I hope this is of some use to you

 

[Jason.S]

To remove immersion heaters, leave the cylinder full, and apply gentle heat round the immersion.

Get your box spanner and hopefully, it should have expanded enough to loosen, with a little bit of grunt

Immersion heaters should always be in 2.5mm 3 core flex as 1.5 is not really sufficient to carry the load.

 

[Torsionbar]

It is OK to wire into the old double pole switch as long as earth continuity is maintained as some older switches had no earthing. The heater should be on its own radial circuit direct from the fuse box and not spured off the ring main or any other circuit. The wiring looks to be outdated anyway and really should be checked over? 1.5mm is inadeqate but was often used

It is quite easy to distort the tank top and tear out the ring unless you are careful and heat it up first (unless it is a sweated/soldered in type)

 

[Marco]

Wow!

I was just saying to my girlfriend that there was no way anyone would have replied yet....but just thought I'd have a quick look and low and behold 3 replies....and all usefull....

Thanks a lot guys.

I got some 2.5mm today in case (or for future stock!) so I will replace the 1.5mm (it's for my girlfriend's parents - so want to keep the outlaws happy!).

I will try changing the thermostat first to see if that does it, but I like the sound of the tips about leaving it full and a bit of heat to break the seal, plus I was only using a flat thermostat spanner on it, but invested in a box spanner today (good old screwfix) as I figured it may come in handy over time!! I was warry of using too much force as at least they have hot water, but if I buckle the tank, a) they will lose the hot water and b)it will be an expensive job and they have trusted me for the first time on this!

Any thoughts on the cupboard switch - is it ok to use the old switch, rather than a double pole? It does at least have a seperate fused connection downstairs.

Thanks again, I'll let you know how I get on.

Cheers,

Marco

 

[Jason.S]

I would replace the switch as well.

Its only a couple of quid.

And make sure all connections are tight, as loose terminals can build up resistance in the cable and cause heat build up.

Good luck and dont force it

 

[Marco]

Thanks Torsionbar, our questions must have crossed in the post!
The wiring is a bit old, but the switch is fully earthed and linked to a supplementary bond, and seems to be on its on circuit. I'll replace with 2.5mm heat resistant from the switch. I'm 99.9% sure the immersion is the srew in type, it was just very corroded. I've suggested they keep giving it a squirt of WD40 'til I get chance to go back next week. But I'll give it a bit of heat as well if needs be!

Thanks again Jason - I was thinking that, but it's nice to hear someone else say it! They might be tight, but for a few pounds, I'd rather it be done right!

 

[Alanka]

One thought: it might be that the actual immersion element is OK, and it's just the connections and/or thermostat that have/has gone open-circuit. This has happened twice to me on jobs. If so, you won't have the dodgy task of removing the element.

You can test the element itself in position - once the terminals have been cleaned up - by measuring the resistance between the disconnected element terminals with a good multimeter. If the element has totally blown the resistance will be pretty well infinite ('overload' on the ohm-meter). A healthy element will have a resistance of very roughly 20 ohms. A shorted element will read practically zero. You can also check if there is leakage from the element to earth, by checking the resistance between either element terminal and earth. It should be practically infinite. If it's less than say 100,000 ohms it should be replaced.

Hope this helps.

 

[MidJeff]

tip on how to remove very stiff immersion. only if it is save to do so is to heat around top of immersion with your blow torch waving heat around top this usually softens any boss white etc.

 

[david williams]

turn of water supply to cylinder,use a proper immersion heator spaner,tap handle of spaner with hamer,i have taken out thousands of these never had a problem,2.5 heat resistant,are you part p

 

[Jason.S]

......are you part p

No need for maintenance, replacement or repairs.

 

[david williams]

i know but in reality we should all be

 

[Marco]

Thanks Alanka - plan A is that it is only the thermostat that has gone and I will just wire in the new one (with 2.5mm heat resistant cable), Plan B to fit the new Immersion using new tips, thanks to all.

David/Jason - I was happy to replace the damaged one initially, as I knew part P was not required for this, but partly for confidence and partly to widen the scope of work I can do, I'm looking to do the Part P course in 2 weeks!

 

[stevetheplumber]

this is im my opinion the best imersion spanner strong cranked and easy to tap round with a hammer doesnt slip like pressed steel one or open up like the box ones
[DLMURL]http://www.monument-tools.com/web_images/72dpi_min500pix_A/MON361.JPG[/DLMURL]

 

[Marco]

Job done! Thanks for all the tips. In the end it was just the thermostat (and I was able to confirm this using Alanka's resistance tip before final connection which was useful).

In the end replaced with 2.5mm heat resistant cable, cleaned up immersion terminals, 20 amp double pole switch and new thermostat set at 50 degrees. Took a lot longer than planned, but I, (and the out-laws more importantly!) were happy with the job! Charged for 3 hours at family discounted rate (!) including time to pick up parts, which I think was fair?

 

[Waterglen]

I do not think that you should be attempting to work on electrics , first not to have any means of testing the element, then to not automatically replace the complete heater when the terminations have almost certainly been burnt, if they have been overheated they not last long anyway. you should get training first.

 

[helpsy]

Another way of removing a really stuck immersion heater is to stitch drill a triangular segment of the body and get some adjustable grips and squeeze the body in tight.....it works a treat believe me!

 

[lbp plg & htg]

Thought in was sure Part P only required when new being installed?

 

[Keefy]

Thought in was sure Part P only required when new being installed?

There's a bit of confusion surrounding Part P at the minute, a lot are still unaware there was a recent change: http://www.ukplumbersforums.co.uk/p...nt-confirms-changes-part-p-building-regs.html

 

[Ray Stafford]

I do not think that you should be attempting to work on electrics , first not to have any means of testing the element, then to not automatically replace the complete heater when the terminations have almost certainly been burnt, if they have been overheated they not last long anyway. you should get training first.

Thread from 2009!

 

[lbp plg & htg]

Didnt even notice that Ray. Lets hope whoever btought it back up gets out to their customers quicker.