Microbore pump speed

[daffs]

Hi
My new system is a Worcestershire Bosch Greenstar 24Ri with a hot water tank and 8 radiators fed by 25 year old microbore.
It's an open Y system with no by pass (one radiator is always on).
The radiators seem much hotter than the old system - they're just about touchable.


But... I have a low hum that permeates the house It's not terrible just enough to annoy.
I found that turning the pump speed down to 1 helps.
It's the cheapest pump that screwfix do
However I searched here and found mention of boiler over heating. So I only left it like that for an hour before losing my nerve & returned the speed to 2, where the installer left it.

The system was powerflushed when installed but when i had cause to remove a radiator there was still a lot of black water that came out. So I hosed through that radiator and got load more.
I put extra fernox in the header tank when i put the radiator back.

So should I try ia lower speed & see if the boiler cuts out?, buy a better pump? hose out all the radiators and put some noise inhibitor or put up with the hum?

Thanks

 

[gas4you]

I would normally leave a pump on a microbore system on at least 2, if not 3.

 

[JPC]

consider some x400 desludger to cleanse the system...will need draining after 2-4 weeks and flushing and inhibiting.
turn the pump down to the lowest setting that will still warm all the rads up.