Flow Noise in CH

[Snippers]

Hi,

I've searched the forum for an answer to this query but no joy.

We've just has a back bolier removed and a new Greenstar 30CDi combi fitted (upstairs). This required some new manifold piping upstairs and new flow/returns to downstairs.

Most of the rad flow/returns are micro bore (8mm) with some 15mm and the new 22mm manifolds.

Since it was installed we have heard gurgling, running / trickling water sounds from the system, mainly our bedroom radiators, when the system comes on in the morning. This lasts around 10 secs and then stops completely.

I have bled all rads and I'm prety sure there are no air locks in the system. The boiler pumps setting is default (4 modulating high, I believe). The rads have not been balanced (yet). All except two (hall with thermostat and towel warmer) have Danfoss bi directional TRVs. One or two of the TRVs hiss a bit when throttling.

I have tried increasing the pressure (now 1.2 bar when cold) and adjusting the bedroom rad lockshield valve positions but the noise is still there.

What should I try next - balancing? Can I reduce the pump head. Despite the microbore, I think the system friction loss is quite low as the pipe runs are fairly short.

Could this noise be due to turbulence when the pump starts up?

Any advice appreciated.
Thanks
Stu

 

[Snippers]

Just checked the service manual - lowering the pump head would mean changing from default proportional pressure high (setting 4) to proportional pressure low (setting 5).

 

[Blooflame]

Had a prob like that recently with a worcester with one of those new grundfos external pumps. The one where u press the + or - for speed. It was gugling, wasn't sure of the prob so reduced speed and all was well. I wonder if the piping is ok on ur system? to ensure good flow I'd fire some fernox cleaner into the system to see if there is an improvement over a week or so. If there is u'll probably need a flush.
Did u have plastic pipework? Just wondering if there's air getting into the system - u know how plastic is

 

[Snippers]

The system is very clean - no sludge or pipework fouling. Cleaner has been through a few times and also just before new installation.

No plastic pipework and system under pressure so no air can get in as far as I know.

If I lower the pump head and it's too low then I may end up with very low flow to the rads furthest from the boiler.

 

[Blooflame]

may as well try it, you might even be successful mate. Sometimes we just stumble over the solution and the theory plops into place!? I really can't imagine what it could be. The pipe size changes must have an effect on the flow, just try reducing the speed if at all possible. Don't think you can on those, unless you put a grundfos pumphead on it with a speed adjustment