airlock in CH system

[barbara]

We recently (xmas) had pump replaced and boiler descaled, and after that all rads were working beautifully. Yesterday the system seems to have come to a halt - only the first two rads in the system are hot, and then only at the bottoms. We have bled everything, but no air or water comes out of the upstairs rads. Water comes out of the downstairs ones, but they are stone cold. We have checked (header?) tank in loft which seems OK.
Boiler is IDEAL E type.
Another small (?) detail is that a self bleeding valve was also fitted somewhere above the pump and that had been spewing water.
The pump is a new Grundfoss and seems to be working OK

Is there likely to be some major airlock somewhere, and what should I do?

 

[ChrisR]

Most likely is that you still have a blockage in the feed pipe where it meets the rest of the system. So there's not enough water in the system to circulate. Flushing doesn't always remove it. It can be so hard the pipe s have to be replaced in that area. Bits can cme loose, move, block pipe... As a get you warm measure water can be got in via the drain point or down the vent pipe, but it takes some knowledge, the right bits and at least 2 people really. Call the flushing people back - what did your contract wth them say?...

 

[oilman]

To get over the immediate problem with the auto bleed valve, you can do up the plastic cap/screw and treat it as manual.

If no air or water comes out of the upstairs radiators there must be a blockage in the supply from the heater tank to the radiators. You should have the pump off when you bleed the radiators though, as the pump can cause these symptoms in some circumstances.

 

[barbara]

thanks for comments. Seems like accurate diagnosis.
not sure how to locate where the feed pipe meets the rest of the system. GUess will have to get plumber if pipe needs replacing.

Some air sometimes comes out of top rads. One heats up fine, the others just gurgle.
Havent tried suggestion of feeding in water elsewhere - sounds rather tricky??
but thanks

 

[oilman]

.......not sure how to locate where the feed pipe meets the rest of the system.

Go to the header tank and find the outlet pipe, then follow it (well that's one way). If the pipe changes floors before joining the system pipes, find the vent pipe, and there may be another one within a few inches of it, that will be the feed and expansion pipe.

 

[krispy]

cold feed blocked