refilling a system-is it difficult, airlocks, etc??

[PaulB45]

i have heard it is difficult to refill a system if drained down, due to air locks getting into the system/pipework, etc. is this true and how can it be avoided? I am replacing my immersion heater this weekend (hopefully)! and obviously need to drain down a lot of my hot water cylinder in order to do this. But I am a bit worried about getting airlocks into my system when refilling! any tips would be useful! ???

out of interest, 6 months ago, a plumber who i called come round and fitted a new Grundfos pump to my heating system. (my hot water/heating started to take longer and longer to heat up and he said it was due to my pump packing up gradually). this must have been the casde as it is much better again since and i have no complaints with it. he charged me in total 246 pounds sterling. was this a fair price?? it only took him about an hour and a half to complete.

 

[twgas]

if immersion is in top of cylinder then its just turn off feed to cylinder, open hot taps and wait till they stop running, (just to empty pipes and confirm valve works). couple of old towels to soak up spillage, then remove old and fit new. job done.

as for pump costing £246, if he drained system and changed valves then he is a tad more expensive than BG. but if you're happy with the job and cost it must be a fair price.