any tips or tricks?,,put your top tip here to share,

Them offset connectors are only good for the scrap pile.

Great tip wetfinger !

Here’s one & I’ve done this a few times.  A prime example for all Plumbers; No air in, no water out!!
Now the boring part first, to work on Unvented Cylinders you must have your G3 Qualifications!!

Now then, & as I said I’ve done this a few times, so it’s no fluke(not the Multimeter).
You can change the combination valve on an UVC without draining the cylinder, EVEN if the combo inlet valve is at the bottom of said cylinder.  Amazing eh???!!!

Turn off the mains Stopcock, Open all taps in the whole house & shut them off again when water has stopped draining out of them.
A Megaflo type unit with the internal bubble will take some time to stop running, so I’d generally just take the pressure off & not let it drain through the taps, as there’s a certain amount of siphoning going on.

Just ensure you close all taps & tell the dafties in the house not to flush a WC or open a tap.  OK, that’s you good to go, disconnect the inlet side of the combo valve first & then gingerly disconnect the cylinder side, replace/repair as required👍👍👍

Oh one Wee last tip on replacement combo valves, Mr Central Heating on-line can supply a generic one for around £35, much cheaper than anywhere else.  For the hard of thinking, the combo UVC inlet valve contains a DCV, 6Bar blow off valve & a pressure reducing valve(reducing the pressure to 3Bar).

I hope that helps, 
No air in, no water out👍👍👍

The whole idea of an Essex flange is to fit it from the outside not through the immersion heater boss.

ok I see what you mean now, thats a good way to fit them, they are a difficult job so using the immersion boss is a good idea, in that video ole plumberpants has the cylinder out and drained, thats a lot easier than doing the job in situ in a tight cupboard with no light and no room to maneuver, not a job for the faint hearted, smiley-sad056 nay

It looked very simple to fit. Excellent job