Noisy pump - what to do?

[Santorium]

Okay, used CH for the first time last night with no problems, come to switch it on today and there's a screaming noise coming from the boiler unit.

No noise with just HW, but wails like a banshee with CH activated.

I assumed that it's the pump sticking and disassembled, removing front disc from pump and manually turning the spindle.

All fine for about 20 minutes, then the screaming returned..

What to do??

 

[BDL]

Change it?

Radical or what!

 

[Santorium]

Change it?

Now where would be the fun in that??

 

[meldrew's_mate]

Put some water in the system?