hubby has lagged the majority of pipes that were banging, but have run out of felt, would it be all right to save buying extra felt to put an old tea towel round the last 8" or so where we think its still knocking ? any help greatly appreciated.
It depends if your pipes are banging due to excess movement or air in the system ?
If its due to movement then it should be fine BUT central heating pipes aren't generaly lagged .They should have proper clamps holding them in place every few feet,these clamps do allow lateral movement as they alter they're length due to heat expansion.If they are banging quite loudly then its probably air in the system.Bleed each radiator in turn and that shoud cure the problem.
You may find the problem to be the ball valve on the central heating header tank, thats if its a conventional boiler. If so its not a big or expensive job to get it changed.