Luke Moreland
Well-known member
No plunger, but I can go take a look.If you have a sink plunger, try plunging the header tank outlet pipe from inside the tank.
Also, it could be your drain hose blocked. Shut off drain valve, take it off and see if water comes out the drain point.
Also, open up all your other rads.
Hose is off, rad drain valve going straight into a tray.