hi Andy
We have installed a check valve and it seems to have worked but we still have to wait for low ambients, which are coming now in the next month. ( WE are in South Africa) gets down to -5*C sometimes -10. Cold for us nothing for you i pressume.

The other advise that we recieved from the manufacturer was to install a P trap near the oil sep and that didnt make sense to me even installing it just below the header it would still migrate when she cycles????