Hot Water Running Cold

I keep having problems with my hot water running cold - sometimes a week at a time I have no hot water unless I use the 'Switch' however at times it will run hot, then cold, then hot, then cold then randomly the next day it will start working normally again with no problems. I have had this happen a few months ago, then it worked fine for a month or so. Then recently it wouldn't work again and has been like this for 2 weeks, then today it's working again!

I'm presuming from similar posts that it might be the heat sensor? But can you confirm this please? Thanks!

It could be a lot of things.
No one can confirm from a key board.
Have you gone through the falt codes?
Mike