sticky boiler fill valve - scale or some other cause?

[Cooper69S]

Gday all
When I turn on my coffee machine (5 year old Isomac Mondiale) the pump kicks in to fill the boiler, but it seems like the valve is stuck as the water is just cycling through back into the tank. If I leave it going it will usually kick in and fill the boiler after a while, maybe a minute or more. Rather than just leave it going, it usually kicks in a bit quicker if I turn it off and on a few times instead. The problem started after the machine sat without being used for a few weeks. Its back in daily use now.

My first thought was that maybe it was sticky from scale build up, although I don't know if they're susceptible to that. I've only ever done one descale about 3 years ago so I pulled out the mushroom to have a look.
There's very little scale on it, but a few lines here and there inside the group head. The gicleur screen thingo had some scale on it and was a bit stuck but not too bad.
From the look of the attached pics, is there any likelihood that scale could cause the valve issue? Is there any point in doing a descale? Or do I need to just buy a new valve? Or anything else to try?
Thanks
Geoff

[Cooper69S]

No ideas from anyone?
I spoke to a service tech who suggested that the first thing to check would be the boiler fill probe in case it had scale build-up that was preventing the machine from checking the fill level. It did have a film of scale over the tip that fell off easily, but that made no difference.

The issue is getting worse too. I didn't mention in the other post but when the sound of the pump is different when it works properly. When its not working, the pump is quieter and just keeps on going indefinitely. When it eventually kicks in and works properly, it's louder and only takes a few seconds.

It seems I can buy a new solenoid for under $100 but it looks like its in an awkward spot so can anyone offer any other suggestion that I should try before I order one? that would be appreciated. Thanks