Radiator gurgling when hot water tap is opened/closed and combi boiler fires up

[jacoscar]

I have been noticing that when I use the hot water in the bathroom I hear a gurgling noise from the radiator (similar to when you’re filling up the system)

I have a combi boiler; I normally hear this noise when I close the tap and I think it coincides with the boiler turning off

Obviously there is some air in the system (so don’t tell me that), but is this a sign of something else not completely right? Like the hot water exchange circuit not completely sealed from the heating one?

 

[ianmcd]

Sounds like you have a dead leg on the pipework some where

 

[jacoscar]

I do actually have two ‘dead’ legs on the heating system; I’ve got pipes in place but radiator not fitted yet (but air has been purged with some temporary isolation valves)

But is it normal to hear these noises if the heating is not in use?