hot water cold rads

[angel hands]

I have a potterton 40el-80el boiler, I have boiling hot water but no heat from the rads, the pump was replaced about 5mths ago & it is still working (i can hear it makin its usual noise lol) I have bled all of the rads & got a lot of air out of the upstairs ones & also I tried to bleed the system. any suggestions as to what it could be.
thanks on advance Carol

 

[kevplumb]

check the three port valve is working hot water position is default

 

[angel hands]

HI
It's not that & the pump is fine apparently I have a massive air lock & need to get rid of that, tried bleeding the system from the rads to no avail, been shown a cpl of other things to try ie open the central nut on the pump as the air lock seems to be near there,