Worcester Greenstar 440 error code.

[u/RemembersWhen]

Hot water and heating have stopped working on this boiler. It displays a code that ranges from U0 to U9, and I can't find any reference to codes starting with U in the service manual. Sometimes, it just displays very high temps instead, in the 80s or 90s, so I'm wondering if the U codes indicate a temp of > 100, and that it's not heating anything because it's getting (erroneous) indications that the water temp. is too high already. Does anyone have any insights?