Boiler not keeping up

I have 2 zones not sure which is which. I do have heat upstairs in my kitchen and my front room but not in the livingroom 2 bedrooms and 2 bathrooms what can it be The boiler does go on and the therostat is in the livingroom. I was told it can be slush in the pipes so I put on the wood burnning stove to see if it works but nothing. I was hoping that you can help me.

If there is an accumulation of air in the upper zone, you won't get any water flow...you may just need to bleed some air out of the system. Depending on how the zone is controlled, are you sure the circulator or zone valve is operating properly?