New boiler - ticking rads with hot water only

[Amelia1730]

Had a new Ideal Logic System boiler fitted recently following final meltdown of old boiler. Following fitting we had loads of air in system which I've slowly got rid of by bleeding bit by bit and awful running water sounds as though rads are half empty when heat switched on. Water fizzing in one rad, which was evident on bleeding, one rad cool all others hot ( initially, one rad hot at top cold at bottom, one rad cold at top hot at bottom). Heating engineer said it may need another power flush but wait a while to see if settles. With the warm weather I've not had the heat on but have tried it for 15 min sessions now and again to see if any improvement.

However, I now have ticking radiators waking me up at 6am when the boiler fires up for the hot water! Never had this with old system. Why would rads tick when heating is switched off?
I thought the days of worrying about our heating system were over when we had this work done. Any advice or comments appreciated.

 

[Nozzle]

It's expansion and contraction as the system heats and cools. Perhaps your previous boiler was incapable of performing properly and now your new boiler works properly you see the effect.

Nozzle