In my distant, carefree, and overconfident yoof I once connected 240V to the low voltage terminals on an early Vaillant.
Cost me half the profit on the job to rectify.
You can't buy experience - or perhaps here I did.
Also: The Tado diagram posted applies to where the pump live is fed from the boiler ("pump run-on"). This cannot be the case here, rather it would be an old-style Y-plan.
"
The pump is in the airing cupboard with the wiring centre.
If I could do this, that would make life a lot easier."...
https://www.electricautomationnetwork.com/PDF/ENGLISH/FINDER/CATEN_13Series.pdf
I read this as : 240V SwL from Tado HTG NO "call for heat"
closes contacts 13 (in) and 14 (out to load), in your case 13 would be permanent live.
HTH Disclaimer: I'm also not a qualified electrician.
Site cred is very much a thing, particularly when new.
It's a very different equation buying tools from a newly qualifide's PAYE wages to the turnover of a self-employed guy 20 or 40years down the line.
Nevertheless I propose the following rigid demarcation ;
Plumbers...
This sort of thing* can be used where a wallplate elbow is set back too far behind the finished surface.
Available in different lengths and may be cut to suit.
* I call it a 1/2" extension piece, but terminology varies
That's good for the element itself; do you also have continuity through the removed thermostat terminals and no reading between thermostat terminals and brass body?
O.P. your installation is no less safe today than it was when newly installed.
No service engineer has found otherwise when carrying out the mandatory safety checks that are a part of every service.
All agree that it is "Not to Current Standards"
Details of NCS here...
With the power off and stat disconnected as in your photo, get a multimeter and test resistances L-N, L-E, E-N.
Also; the photo seems to show water staining on the casing from above and above right of the 'mersion