Vailllant ecotec plus 937 - fault code?

I had a power cut and switched off my boiler (ecotecplus 937). When power was restored I put it back on and the fuse blew. I changed the fuse and put the bolier back on. I thought it was fine but now I have 2 fault codes - F81 and F91. I basically have no hot water. Do you know what the fault code means and what I can do? I've already tried the reset button.