header tank over flowing

[malc]

hi all, i recently cleaned a central heating system, left sludge cleaner in a couple of weeks, then went back to drain, flush, and re-fill.
now when boiler is started, the header tank over flows within about 5-10 minutes.it does stop when boiler is turned off. i`ve taken some water out to drop the level, but it still happens.
its an old system but boiler is fairly recent, hot water is gravity, heating is pumped.
any ideas greatly appreciated thank you.

 

[Last Plumber]

If its expanding water that overflows, the level in the tank is too high.

How is the water rising ?

Up the feed and expansion or over the vent ?

 

[malc]

thanks for reply, i haven`t been back yet, but it wasn`t overflowing before i cleaned it, and i have taken water out of the tank to drop the level. going back in a few days so will check where its coming from, but wanted to have some pointers before i go.

 

[Last Plumber]

Well check how its filling first and then come back to us.