Ok to change price right before contract?

[Marci Stein]

So my house was listed at 219 k, and I agreed to sell at 205 , as is. 
called plumber to turn on heat and hot water for inspection , but the heat did not come on (after I paid him $1000 )

I would like to charge the buyer $1000 more . I now have to buy a new hot water heater.  contracts were sent to lawyers, but not yet signed. 

Has anyone ever done this ? not sure it is the right thing to do and if I lose this buyer, I am not concerned I will charge more for the next one. But the realtor, a friend will be upset.  
thx very much .