Problems with brewpak boiler

[Kilgore Trout]

Tried a brew last week using my brupaks, 2000w, boiler (plastic) and it just stopped heating after about 20 mins. The element was cleaned after last brew and again before starting, I know that build up can make the boiler 'think' it has boiled dry. It cut out at about 92 degrees twice (each time I emptied and cleaned the element, which was still pretty clean) before finally getting to the boil. Then went for 20 mins before cutting out. The boiler is about 1.5 years so out of warranty and worked okay for 15 or so brews far. Anyone else had similar problems or any ideas of solutions? Please don't say make sure element is cleaned, it is.

 

[Covrich]

Probably stupid suggestion as you may have covered this but when you say cleaned the element.. do you do a descale??

 

[Kilgore Trout]

Yep. Not at home at the moment, but I think the stuff I use is called
Chem(i)pro. Any suggestions on a better cleaner/descaler?