New boiler installed, now I can only get one radiator at a time working

ThisIsWeird

If not too late, what you can try is to lower that bare magnet into the water, and leave it there for 10 minutes - see what coats it.

markin

Trv should be wide open to balance the system

Mr_s

Just an update if anyone is interested.

I had a little bit of a think back and I'd bled and re-pressurised the system a few weeks prior to all of this and it turns out, attempting to operate in the dark I'd turned the wrong valve and almost closed the valve inbetween the ch return pipe and the boiler, hence why the water was not flowing around the system optimally. Oops.

Good job boxt didn't get anyone out to me isn't it.