Noise from radiators - unbalanced or air-trap?

[speakermonkey]

About this time last year, I installed some lovely new cast iron rads, replacing the previous old skool skirting heating. The strange piping takes some explaining so bear with.

The original pipes come out of a wall sketched on the right hand side of the pic. I needed to run new pipes behind plasterboard to get the wall plastered and do the rads later, and so guessed (wrongly) their position by bringing the flow up to meet the return and temporarily terminating with ball valves* so I could re-prime the system. When the rads arrived, I realised they needed to be much lower, so I rerouted both down. This means that the for aound 1.6 m, the flow pipe is elevated from the rest of the circuit by 150 mm. Short of cutting open the newly finished wall, there's not a lot I could do about this. So I thought I would just suck it and see.

The noise I get is a kind of clicking, tapping, dripping noise (no gurgling) which occurs about 20 mins after turning on the CH. I have balanced the rads and turned the pump down to minimum flow as I understand old pumps can let in air. The rads heat up evenly and quickly and, most importantly, they do not let out any air when bled!

Do we think I have air trapped in this raised section and is there anything that can be done that doesn't involve cutting into the wall? Surely once the system is primed, no new air should be let in?

or do I need to rebalance my rads properly?

I have tried to capture a vid of the noise, but much like a watched pot never boils, every time I turn on the camera, the noise stops.

*I have kept the ball valves as I will need to drain this heating circuit again to fit rads into the last room. This will allow me to do this without draining the whole house. Once it is all complete, I will probably remove them.
Also, don't worry about the scorched wall, this is an ongoing renovation project as you may have guessed.

All contributions appreciated.

 

[Dereekoo]

I would definitely say you have air trapped in that section of raised pipe but to what extent??. Possibly if you had the pumps at high speed it would push the air out and into the radiators for bleeding off but I would also imagine that the isolating valves are severely restricting the flow through the pipes and not allowing the air to be pushed along (unless they are full bore ball valves?) A tee with a valve on top somewhere on the raised section of pipe so you can bleed it like a radiator??

 

[Madrab]

If your system is sealed then unlikely to be air, CH system pipework rises all the time in systems and won't create any noise. The ISO valves aren't a good idea, they aren't design for CH and can suffer for it, they can also create turbulence due to the reduction in bore size. Does it stop if you shut down the valves?

Clicking, ticking tends to be expansion/contraction noise though that would usually be created by pipes touching or radiators sitting on metal brackets etc.