Connecting a Magna Cleanse to radiator valves

I've just acquired a Magna Cleanse (MC) to use with a rental property I have that has a Magna Clean. Before I go to the rental property, I wanted to do a trial run at home. At home I don't have a Magna Clean due to the boiler F&R pipes being in a wall and boxed in and the boiler is outside on a wall. So keen to avoid redecoration around the boxed in pipes and I thought perhaps I would have some success by taking a radiator off and connecting the Magna Cleanse there. Certainly the radiator I took off had a lot of sludge in it, but after connecting the MC there I saw no flow through the clear pipes, all I could see was dirt suspended in the water not moving. I appreciate connecting at this point is suboptimal but surely I should get at least some flow. Valves are not blocked since water flows out of them. The only other thing I can think of is that I've introduced an air lock into the system, the MC was getting hot'ish (~40C) but I suspect that was purely via conduction rather than flow + conduction. All the remaining radiators were heating up okay.

I have a spare circulation pump which I might connect up to help with flow (hopefully I'll get it the right way round!)

I'm keen to learn how to do this for the future. Currently we simply drain down every few years and dose with inhibitor (although clearly from the look of the water we need to do it more often). What can I do to make connecting at this point with the MC work?

1. Perhaps the MagnaCleanse presents a relatively high resistance to water flow, so the water is merely flowing through the other radiators as an easier option.
2. You need to fit it to flow or return, preferably return, near the boiler so that all water in the system flows through it and does not just bypass it.