Problem with Vokera boiler - flue and pressure?

I have a couple of problems with my Vokera Synergy E boiler which I was hoping someone could advise me on please.

The error code keeps flashing red saying there's a flue problem. which means it turns itself off - if I reset it and turn it on again it sometimes works for as long as you want, and sometimes gives up after 20 mins with the same error code. Any ideas?

Another problem is the pressure keeps falling over about a week from 1.5 to 1 bar though no evidence of leaks anywhere (have seen other advice on this on here - will check out those options). But any other ideas?

Thanks v much