Codensate and Carbon Monoxide

I can't comment on the particular model of boiler, but it's very commonplace to have condensate running into a standpipe or whatever inside the house, ie open to the atmosphere - I've seen this arrangement in manufacturer's installation instructions.

On my Valliant there is a trap on the condensate outlet within the boiler.

VERY unlikely. Most half decent boilers have a siphon trap and the casing runs under negative pressure if the manufacturer used sense in designing the unit. I think the cdi fan extracts from the combustion chamber but would have to check as I have not serviced one of that model.

I have never seen one like that, however i have seen one that empties into a condensate pump unit and I don't think they are room sealed. I have seen one that went into a 40 mm sink drain pipe but it had a one way valve fitted, probably because the pipe was connected to a Saniflo.

Just FYI my elderly Glowworm runs the casing at positive pressure. The combustion chamber is entirely surrounded by this positive pressure except where the flue goes outside - so leaks are of fresh air.

Andy