Bought a Tempur mattress and pillows about 3 years ago due to back problems, wasn't cheap but best money I've spent. No more back pain, worked a treat for me and comfy as.
Not worked on enough VIessmann boilers to really say if they're good or bad. Just checked online reviews and the consensus is the majority of customers think they're garbage and the installers think they're brilliant.
Vaillant Ecotec all day everyday. As for the Greenstar 37 or 42 not being up to the job, nonsense. Sounds to me like the builder has a contract to fit Viessmann boilers or can get them at a price to make it more profitable.
+1 for Vaillant( Ecotec range) Take some of the advice on here with a pinch of salt as it's obvious some of the people giving it haven't got a clue what they're talking about.
Ventilation for a room sealed boiler if required is for cooling of the appliance not to aid combustion as the air for this is taken from outside via the flue. I wouldn't worry too much about the safety aspect if it's regularly serviced just make sure the carbon monoxide detector is working at all times. As for the noise I don't think the CDI range are a particularly noisy boiler maybe the pump or fan is the cause of any undue noise?