fuse blowing, baxi 105he

Hi,
I have just replaced the o-ring on the dwh diverter valve on my boiler.After running for approx an hour, the fast-blow 2A fuse on the PCB blew. I replaced it but again after a while running OK it blew again, I replaced the fuse again and is running OK for now, but I'm sure it'll blow again.. I can't see how the 2 things are related, but other than replacing the PCB (a cost I could do without right now!) I'm struggling to understand it. Do you have any ideas?

Thanks & Best Regards,

Dave Robbins

Either water has got on to an electric component (which may have now dried) or possibly fan or pump taking fuse out when hot