Be aware that if the immersion stats are set low and you raise them to 60/65° then your electricity costs will increase also.
But it's always going to be a balance between cost and comfort - such is modern life.
What's the main issue here?
Air in the rads or rooms not getting to temp?
Boiling hot rads are not conducive to warm rooms.
Do some heat loss calcs and see if the rads are up to the task.
Is all the pipe plastic and what bore is it?
It's should say barrier pipe on it or have some...
My tuppence worth...
All new rads, boiler and pipework!
And the water is orange!
Something ain't right.
Is any of the pipework plastic?
Is it barrier pipe?
If not, it can draw oxygen in through the walls.
Fit the aerator first and see how things go.
There's more to being a plumber than just charging, for what some DIYers believe they can do themselves.
It all seems easy in theory!
Even I (a seasoned plumber) sometimes wish I had 2 extra, double jointed, wrists and elbows!
As @Razor900 and @muggles
Get the same controls and cylinder as the boiler.
They will all be under the same warranty and will work more efficiently together.
System has to be designed for low temp circulating fluid as per building regs.
Servicing a UV is a 10 minute job done same time as...