Britont SE80 - Fault Codes?

Hi,
I moved into my property 2 or 3 weeks ago and boiler has been working fine up until now. Around a week ago I decided to attept to set the timer on my boiler. Even since I have been experiencing a variety of issues with it.
First the central heating would switch itself off (hot water would remain on) and I would have to reset the boiler to get it working again (I had to do this ever day for 2 or 3 days). I though this had been caused by me timing it wrong so I set the timer again and switched the boiler on and off at the mains and all was fine.
Problem gone I thought... but that was about 4 or 5 ago and yesterday I got home to find my heating and had water had both turned themselves off and boiler was displaying fault codes 70 & 80. I reset the boiler and all ok for a few hours... then same thing happened but this time boiler displaying fault codes 40 & 80 flashing.
I have read that a common fault with these boilers is a defective PCB unit and judging by the fact I am having different error codes almost everytime it turns itself off I am guessing this is the case here.
How difficult is a PCB to fit? Would I be able to do it myself? Is it a case of just disconnect old one and putting the new one in its place?

If not do you have any idea on labour costs involved (have alreday priced up the part).

Any help much appreciated!!

Thanks