Need help downstairs rad problems

[hiretools]

hi everyone i just wandered how comes my rads downstairs r struggling to come on even though i have changed the pump and changed the two gate valves at the top and bottom of the pump.I have turned all the vales on both sides off upstairs.the downstairs radiators i opened the LSV fully on one side and on the valve with the numbers set that at number 3 ish they came on and stayed hot. (gr8 i thought) then i repeated the process upstairs but only put them on number two on the numbered valve but only opened the LSV valves a couple of turns this worked until i turned the heating off to deal with low pressure on my hot water when i turned the heating back on bang i was back to square 1 with the rads downstairs any ideas any one i have a grundfos 15-50 130 pump a honeywell thermostat st699 also a motorised honeywell v4073a1390 3-way valve and a thorn boiler plus a copper cylinder with header tank in the loft.

 

[fireblade]

sound like an airlock shut all the upstairs rads run the pump on full make sure your diverter is over to heating when you refilled the heating you should have locked you three port over with the lever on the side to vent the heating sytem when the downstair rads start working put the upstairs ones back on

 

[hiretools]

Thanks for your reply 1 more thing though. Does the LSV valve have to be fully open or can they all be on different settings?

sound like an airlock shut all the upstairs rads run the pump on full make sure your diverter is over to heating when you refilled the heating you should have locked you three port over with the lever on the side to vent the heating sytem when the downstair rads start working put the upstairs ones back on

Thanks for your reply 1 more thing though. Does the LSV valve have to be fully open or can they all be on different settings?

 

[fireblade]

the lsv are all different hence the one nearest the pump shut down the one furthest from the pump fully open all the ones in between open a bit more than the last one if on rad get red hot straight away shut it down to make the hot water go tothe other rads