The revelations were made public in the Newsletter newspaper
There are further explosive allegations regarding the mis-managed green energy scheme.
The Newsletter is claiming the former Economy Minister ignored calls for cost controls to be put in place - soon after the RHI iniative was set up.
The newspaper claims to have seen documents from civil servants pointing out concerns to Arlene Foster that costs could spiral.
Yet, the staff say the former First Minister didn't act on their advice.
Mrs Foster has always said she was not warned of any potential costing implications.
She has also supported calls for a public enquiry into the scheme, and says she will be proven innocent at it's conclusion.
Social media warning ahead of inquest into death of Noah Donohoe
Former senior police officer Jon Burrows confirms UUP leadership bid
Man’s body found in Cookstown in search for missing 21-year-old
Two taken to hospital following suspected gas explosion in east Belfast
Man critically ill in hospital following road crash in Co Tyrone n