blocked cold feed

28 Feb 2005
Reaction score
United Kingdom
What is the best way to check for a blocked cold feed on a vented system
(S plan)?
Also what is the best way to clear the blockage?
Sponsored Links
It most often occurs at the Tee where the 15mm f&E pipe joins the 22mm or 28mm circulating pipes near the pump or cylinder.

It is often a blockage of black magnetite that needs to be cut out and a compression tee fitted in its place (sometimes with new pipe stubs). If you are lucky enough to have a compression tee there you can undo it and poke it clear. You will need a chemical flush to get out the rest of the much that is floating round. If you have the money handy this is a good time to fit a magnaclean which traps the black circulating in the water.

If it is black magnetite in the blockage you can sometimes feel it with a magnet held against the copper pipes, as the magnet will be attracted to it.

I have heard you can sometimes dislodge the blockage with an Aquavac on the Vent pipe.
Thanks for your suggestions JD.
As an alternative could I cut the 15" pipe just above the tee (to replace the tee would not be easy due to lack of access) and poke around with something suitable?
You could try that, but it means you will have hard lumps circulating in the water that you need to flush out.
Sponsored Links
Next thing after the feed should be the pump, where you could get access. A thin drain-cleaning spring can clear it.
SOmetimes the Aquavac (or the mains) works becasue the blockage is jellylike or just "sludgy".
Thanks Chris
I think we are talking about a black jelly here, I cleaned out the expansion tank at the weekend and there was loads of it.

I also drained a rad but it seems to have refilled, I don't know if it's taken water from the exp. tank or taken it from elsewhere in the system?
going back to the origanal question its best to check if its blocked before you do anything else open a drain of cock and drag some water through if the f + e tank ballcock runs the cold feed isnt blocked
The black jelly is the result of a gallon of inhibitor being dumped into header tank without partially draining system to pull it through

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

Sponsored Links