Hot water tank Immersion heater

[plewlandsbob]

Just got back , from a couple of days away,to discover, there is no hot water. The tank and elements are 30 odd years old. Is there a way to test the elements and do you replace the whole unit

Tia Bob

 

[pedrobedro]

, , . . It's scrap, replace the immersion heater unit. You'll need a big spanner, about 86mm but check yours as some vary. , , , . ?

 

[brightspark]

probably be the thermostat knackered ,check it 1st .power in and power out to element look to see if the wiring conections inside arent burnt as well

 

[Seadog]

And check the connections in the spur.

 

[Kayos]

Also, drain the header tank but leave the cylinder full, going to need the weight to undo it after 30 years

 

[Seadog]

And be VERY carefull. It more than likely is well corroded. You could end up buckling the tank. Lots of heat will help, once you've removed wires and a plastic pieces.

 

[tom2207]

check to see if theres a thermal trip on the top ,, just a wee button to press and it goes click ,,, obviously do it with the power turned off ,,, they are easy enough to meter too , just look for continuity .

 

[Dave-sparks]

. Is there a way to test the elements and do you replace the whole unit

Yes there are ways to test the element.
The first and most simple thing is to test continuity of the thermostat, also check for a thermal trip on it. The thermal trip can sometimes be a button that looks like a tiny little dot of plastic with a spot of paint on it so have a proper look at it to see if there is one.
You should also check that power is actually getting to the immersion heater, check fuses/circuit breakers etc.

As for the heater itself you can test the resistance of it from the live terminal to the neutral terminal, it should be somewhere around 17/18 ohms for a standard 240V/3kW heater.

If you have a suitable tester then you can test insulation resistance to earth from the element, this will show whether the casing of the element has split or not. If it is in very bad condition you may find you can get a reading to earth with a normal resistance test.

 

[waddycall]

If you need to replace the immersion heater and can’t undo it try tapping on the flat nut faces with a hammer all the way round. As Kayos says just drain it enough so the immersion is above water level as this will support the cylinder as you try and turn the immersion.

 

[Olderisbetter]

I normally leave the tank as full as i can as already mentioned but i put the gas torch in the immersion collar as they tend to stick, also modern replacement seem fail quicker so i use the inox ones.

 

[cobox]

Don't put too much force on the spanner when unscrewing or or you will rip the boss out of the cylinder (tank). If it won't budge, drill a hole through the top and saw it from the centre to both edges, being careful not to nick the threads on the boss. Replace it. They only cost around £20 including the stat. Beware of cross-threading the new one. Put a smear of Boss White on the washer, and don't do it up too tight. You can always tweak it if it weeps on re-filling. If it goes into the top of the cylinder, you can make things less messy by draining a bit from the cylinder (drain tap near base). If it's a side entry, you'll have to drain all or most of it.

 

[hunter27]

If you buy a spanner for the job and the flange is not recessed get a flat ring spanner (even if you have to skim off a bit of foam insulation). The problem with the box type with a bar through is the bar is not aligned with the flange and if the immersion is in tight, causes a twisting motion especially if it needs tapping around to get is started which it likely will.

 

[steveo3002]

im no expert on these matters

i heaved on mine with the proper spanner and decided i didnt want to push harder ,so i used a small drill to drill in a mercedes badge pattern inside , you could then break out 3 wedge shaped bits fairly easy , saves cracking the tank /hassle

 

[plewlandsbob]

Thanks for all your advice guys. I will investigate tonight after work. If it needs replacing, that sounds like a job for the weekend.

 

[cheb]

I made a better, IMO, spanner. It used three flat spanners, two welded together to provide twice the surface on the sides of the nut, and another with the handle cut off welded at a quarter turn twist so the spanner can be pressed postively onto the immersion heater whilst tapping the spanner with a mallet

 

[brightspark]

he hasnt checked the thermostat yet ,.might not need a new heater