Immersion heater replacement in unvented system

[eternaloptimist1]

I am going to tackle this job tomorrow. Have read many posts here for replacing the element, and am reasonably confident of successfully removing the element and installing new one. Only want to be certain that there are no untoward issues with draining of the system and refilling, because of it being an unveted system with pressurized expansion tank, which has a car tyre type schrader valve filler.

As far as I can see, all I need to do is to turn off the cold water inlet, open all hot taps, open the drain valve at the bottom and let it run out.
Questions are:
1. Will the pressure vessel lose the pressure when water is drained?
2.If so, I will need to repressurise the expansion tank when filling up the cylinder, otherwise the expansion vessel will get filled with water!

The system is the unvented Range Tribune HE, and is installed with all the safety features, none of which will be altered in any way. I see it as a straightforward job, but may need careful repressurising to avoid the expansion tank filling up with water!
Any advice will be highly appreciated.

 

[eternaloptimist1]

Decided in the end not to do this myself. However, if I had the correct part I would have. Just for the record, the immersion heater on this, and I believe most other unvented cylinders, has to be different from the usual immersions you can buy from stores like B and Q etc. I think it has to be constructed to withstand the high pressures that prevail inside unvented cylinders, and to stop people from fitting incorrect ones, the diameter is one and threequarters inch, versus two and a half inch diameter of the usual ones.

 

[JamesTheakston]

usualy immersion heaters are 2 1/4 inch diamteter but as you said, unvented controls are special and specific and you can't mix and match and install any old part on it

btw about the expansion vessel - when you drain down the charge in the vessel will be the same when you fill it ... draining down and re-filling will have no effect on the expansion vessel pressure (as long as it is not faulty in the first place)!!

 

[eternaloptimist1]

usualy immersion heaters are 2 1/4 inch diamteter but as you said, unvented controls are special and specific and you can't mix and match and install any old part on it

btw about the expansion vessel - when you drain down the charge in the vessel will be the same when you fill it ... draining down and re-filling will have no effect on the expansion vessel pressure (as long as it is not faulty in the first place)!!

Thank you for your comments. I found out a bit more aout the pressure/expansion vessel. Inside the presssure vessel, is a pressurised bladder ( a bit like football inner tubes), which stays inflated, so there is no problem, so long as that is functioning ( and one should check the pressure in it once a year) in conjunction with checking the thermal and pressure safety valves.

 

[oilman]

I am going to tackle this job tomorrow. Have read many posts here for replacing the element, and am reasonably confident of successfully removing the element and installing new one.

Is this work, or for yourself?

If it is for yourself, 1) you should not do it, 2) If anything happens it's your pidgeon.

If it's work, from your questions you do not know anywhere near enough, and it suggests you are not G3 certified. In this case it woulod be irresponsible to do the work.