Drained the CH system last weekend (gravity primary, pumped heating, original 1964, extended 1995), fliushed and refilled including bottle of Superfloc. Ran it for six days. Drained again today - bit grey! - refilled to flush through, but the upstairs rads. won't fill completely now, all stopped at about halfway full, even with bleed screw out, no further filling. Never known this before. Anyone any idea what may be causing this? I'm puzzled.
Airlock somewhere - in my diy experience with old systems you often have to repeatedly run the pump and boiler then re-bleed. Also, try turning off most rads so that the full pump pressure is directed towards the area where there's no flow - it'll eventually blow the bubbles through if you keep going.
Sounds like some crud is blocking the feed pipe from the F&E tank into the system. This could be some scale which has been released in the flushing exercise, and has settled there. Someone reported something similar in this NG only a few days ago. Try back-flushing it by feeding mains in through a drain point. You'll probably have to block up the vent pipe temporarily.
[I'm assuming that there *is* water in the F&E tank, and the ball valve isn't stuck shut? That *shouldn't* be a problem since you've obviously exercised it recently.]HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.