I have seen a bumblebee going into an air ventat the front of the house. Is this normal and will this cause a problem? I could block the broken part of the air vent but will this kill them?
I contacted you last year as I had a nest in the compost heap and would like to encourage them to us it again.
You are lucky that you have a nest.
Bumblebees will nest wherever is suitable, so in an air vent is not particularly unusual. I cannot see it causing any problems at all and now that you know it is there, as long as it survives, you can enjoy watching them come and go.
If you block the broken part of the vent and they cannot get in or out another other way, they will die.
Have you any idea what species they are ?