Cold water from triton Martinque?

i have a Triton Martiinque which is only giving cold water.

I had someone in to fix it ,and he said he would have to order a part and come back.As a temporary measure he said he would drill thru a part and fix it back so I could have some hot water whilst he waited for the part.

I haven't been able to get hold of him again , which part could he have drilled thru? I have opened it to have a look but cant see the part that he was talking about