draining rads to try and solve prob, but tank still full

[ribs]

Thanks everyone.... found the blockage in an 'S' bend on the feed pipe, just before the immersion tank inlet. Managed to clear it with a length of wire fed in from the tank in the loft.

I'll leave the heating running (on and off) till the weekend, then drain it again and put in the Fernox. Then look at your suggestions for preventing the problem from happening again.

Thanks again.
Ribs

 

[JohnD]

have you got a Cleaning Chemical mixed in, to break up the sediment? A plain water flush is fairly ineffective, and you now know you have lumps in there.