Unfortunately this seems to be the case with most water suppliers.
We work in 3 different water suppliers area's all are now on 'direct emergency call out to stop taps'
When I asked Yorkshire water to define dire emergency they said uncontrolled leak flowing out of house door!.
Anything is possible but by time you have identified existing valve and bought a identical valve as you won't be able to get parts just easier to swap valve.
Combi or sealed system or tank feed?
If first 2 just drop system pressure turn off other rad valve old towels on floor and swap valve minimum water to deal with.
If tank feed either drain down or if big system freeze.
You could actually probably get that open with a decent pair of grips .
Carefully expose the pipe under connector it may be in a duct depending on how old service is.
Certainly adding some decent pipe insulation would do no harm.
The short section of blue pipe looks to be mdpe that's no problem.
However I would be investigating the connection below it see what it's connected to.
Unless your competent to deal with any sudden leaks maybe get a plumber in.
File or hacksaw end of a key to make it flat brass keys are better.
Though we would just turn valves off and put a container under valve and loosen nut on rad tail.
Unfortunately pic don't show enough pipe to Identify it.
With luck with rad out of way you may find writing on pipe.
Ideally you need to identify existing tube so you can use correct insert.
It is marked every mtr by manufacturer so you might get lucky.
Most site new build will probably be wavin (hep) John Guest (speed fit)
Or polypipe.
But just because you see say hep fittings that's no guarantee it's hep...
Which model Grant combi there are several.
CH will not work if there is a DHW demand which DHW pump running suggest there is .
If you have a multimeter and are competent to use it check if there is a live feed back from flow switch.
Have you have checked there is a live feed to board to the heating terminal 19 and if so a feed out to heating pump on terminal 6 ?
Is the heating switch on boiler in correct position
If board is suspected talk to Grant technical they will walk you through tests necessary.
They really are...
If your looking at the copper tectite fittings (sprint) they are non demountable.
Tectite classic fittings (brass) are demountable.
As has been said great in a tight spot where press gun won't go.
In a emergency they will come apart using a adjustable spanner to push collet in.