Immersion size

2 May 2018
Reaction score
United Kingdom
My indirect HW cylinder has a top mounted immersion element labelled “Shel CODE XB270”.
Does anybody know how long this is?
The cylinder says “Max length immersion 760mm”. I suspect that the one fitted is much shorter than this and is only heating the top portion of the cylinder.
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they are often about 28" long. Purely as a guess, I think maybe yours is 27"

does it look quite old? What colour is the cylinder? A photo of the round cap might spark some memories.
See attached pics, thanks.

I wondered if the 270 was mm i.e. 10.5 inches.

There was a little Shel product leaflet tucked into the top of the cylinder. It only mentions thermostats of three lengths: SS7 (7") SS11 (11") and SS18 (18", no surprise!). There no mention of an XB270.


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Looking at other Shel immersions, the model number seems to have some bearing on it's length, so I'd hazard a guess the XB270 is a 27" version. The cylinder will heat from the top down, how long is the immersion on for at a time?
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Even when the immersion is on until it stops (i.e. its internal thermostat turns it off, which I can tell because I have an electricity monitor) there isn't a full tank of hot water. Most of the time we heat water by gas and that does give a full tank (because the coil is at the bottom, obviously), but I have Solar iBoost, which shunts any excess PV generated electricity through the immersion, and I was seeing if I could get a full tank using that.
I have tried adjusting the thermostat on the immersion. I've emailed SHEL to see if they can tell me what the model number means.
Does beg the question if that is the right immersion, if someone has stuck an 11" immersion in the top of the tank, it will only ever heat the top 11" of the tank. Out of interest do you know how long it's on for before it switches off?
Size does matter, despite what some say.

27" will just about give you a decentish bath when mixed with cold, 11" will struggle to fill the kitchen sink twice.
Polesapart, I would - but the immersion element is inside the cylinder so it's kind of difficult to measure it! That why I asked the question of whether anyone knew the model number.
Heat cylinder from cold with immersion only. Measure volume of hot water at tap before it runs cold. Measure cylinder dimensions allowing for external insulation. Calculate "h".

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