how old is the boiler? if its new, the main things that will give you grief will be the agitator arms being left out when the fuel store is filled, this can be a ballache to clear. other issues weve had is buffer,return sensors.they are PT1000 sensors and readily available, We have changed a couple of lambda probes but thats about it on our boilers and they are about 3 yrs old now. Be carefull of doing software upgrades as they can knock the timing out on the fuelling and without the developer code you cant change it back!!. Get them to have it connected to the internet and set up the remote access through
www.meineta.at . you can see what the issue is before leaving home and it may be something that can be sorted without a site visit.