vokera maxin keeps locking out?

Hi

I have a vokera maxin which keeps locking out.
this is regardless of whether the heating is on or you are just running hot water, there is no time limit on how long it takes. you could be half way thru a shower or it can happen when you initially turn the tap on.

a few weeks ago the water came out red hot and sometimes the heating does not get as hot as normal.

can u help ????????