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[I_want_an_Omega]

Ok, I need to change my immersion heater & have never done one before.

I assume that I need to:

a) switch boiler off
b) switch off cold water feed to header tank
c) drain system of hot water

Before unscrewing the heater (after making sure power is off) is there anything else I need to do?

I understand that there are various lengths of heater available. The label on the tank says:

1450 x 450 and has a note next to it saying heater length less 200mm.

Thanks .................

[Richie London]

My mother has just had her immersion heater changed after 30yrs and it trips off non stop now so make are you get a decent one.

[Shackeng]

You shouldn't need to totally drain the tank, just isolate the tank and run 2 or 3 gallons out as the IH should be mounted vertically in the top, if in doubt, then yes drain it all out. You will need a new washer to go with the heater. Length of htr depends on how much you want heated, but if it says 200mm go with that. I am in a two person household, and only use a short one, can't remember the length but it is sufficient for two showers at once. Once fitted, allow it to heat the water and adjust to the required temp on the top of the fitment, they are never very accurate. 

[STMO123]

k

Ok, I need to change my immersion heater & have never done one before.

I assume that I need to:

a) switch boiler off
b) switch off cold water feed to header tank
c) drain system of hot water

Before unscrewing the heater (after making sure power is off) is there anything else I need to do?

I understand that there are various lengths of heater available. The label on the tank says:

1450 x 450 and has a note next to it saying heater length less 200mm.

Thanks .................

Point B there Robert, you need to stop the water feed FROM the header tank not TO it or the cylinder will fill up from it. The cylinder is fed by gravity from the header.

[STMO123]

Also you say heater LESS 200mm. That's only 8" and won't be the length of the element, it would only heat the top 6" of water. I'd wait until you get a plumber on here (there are a few I believe)

[martin42]

need new emmersion,stat,boss white,proper emmersion box spanner
turn of water to cylinder,via gate valve,if seized then you will have to turn main stopcock of,drain down header tank,then drain down cylinder,either 1 of 2 ways,use drain cock fitted at bottom of the feed pipe from tank,or remove the vent pipe and insert hose and syhpon out water,once drained remove old emmersion being VERY careful not to twist where it is screwed in to or you will land up replacing the cylinder,get new emmersion,apply boss white to the thread and flat surface,fit washer,and apply boss white to the surface of that,then refit but dont over tighten,connect up electrics,fill up with taps open to prevent air locks,once water comes from taps close them allow tank to fill and turn on electrics 

[PhilRich]

You need a 27" (675mm) immersion heater element. Tie up the ballvalve on the cold water storage tank (or turn off the water at the mains whichever is easier for you), You can then either run the hot taps until they run dry & unscrew the old immersion, preferably with the correct immersion box spanner, but beware there will be a fair amount of water between the top of the cylinder & the immersion boss so towels required to catch spillage! Or do it properly & attach a hosepipe to the drain cock which should be fitted at the bottom of the cylinder where the cold feed enters it & empty the cylinder partially so the old immersion can be removed without drama Clean off old gunk from the boss threads, fit new immersion element with a new fibre washer & a smear of pipe jointing compound if you want to be absolutely sure of no leaks Close the drain cock, refill the system & Bobs your Uncle etc.
Please make sure you remove the fuse from the Mains isolator switch before touching any wiring & don't refit it until after the cylinder is refilled completely

[I_want_an_Omega]

Thanks all - much appreciated ............. 

[tigers_gonads]

Is the element in the top or bottom (side) rob ?

[I_want_an_Omega]

Is the element in the top or bottom (side) rob ?

It's on the top - almost anyway. At the very top is the hot water takeoff, the IH screws in next to that so will be at a slight angle - if that makes sense?

[STMO123]

Is the element in the top or bottom (side) rob ?

It's on the top - almost anyway. At the very top is the hot water takeoff, the IH screws in next to that so will be at a slight angle - if that makes sense?

Sounds like a bog standard cylinder,  you should be ok with it

[tigers_gonads]

Is the element in the top or bottom (side) rob ?

It's on the top - almost anyway. At the very top is the hot water takeoff, the IH screws in next to that so will be at a slight angle - if that makes sense?

As philrich says rob.
27 inch element.
Best to change the stat at the same time.  This is located under the cover.
Turn the water off and drain down to about half way 

Beware .............. the threaded coller that the element screws into is braized on and if the tank is hot, i've known the weld to break away so be gentle when you idiot it with a hammer  unscrew it