Blocked 15mm pipe

[Arkwright]

Hi

I'm pretty certain the feed from my central-heating attic tank down to the boiler/rads is blocked. [Why? (1) Because when I drained the entire system, opening all rad bleed valves, the tank was still full ! (2) because having refilled through the draincock (system now running but there's air in there) if I try to bleed upstairs rads they hiss for a while then teh hiss gradually peters out - bleed valve still open, no air, no water].
Also I took a plunger to the water outlet feed *inside* the tank and with vigorous plunging finally got the odd gurgle of water to enable more bleeding of rads - but this was fleeting - helped a little but still blocked. (Well - that's my guess). I alos tried shoving an auger down from inside the tank - but there are 90degree bends.... so I can't.
I know I need (once I've removed the blockage) to flush out the system and put something in to stop it happening again - but how do I remove this stubborn blockage?
Hope you can help !! Many thanks.

 

[nickso]

cut out the blocked bit and replace it. its the only way to do it properly

you could try mains pressure on it but i wouldnt recommend it

 

[JohnD]

The blockage is very very likely to be at the tee where the 15mm pipe joins the large circulating pipes, this is probably close to the pump. It is a common problem. You will have to cut it out. If you replace it with a brass compression tee then it will be much easier to open if it ever happens again.

If you hold a magnet against this clogged tee you may feel an attraction to the iron-based black corrosion material inside.

As well as cutting out the clogged part you can poke up the pipes around it to loosen anything there, then flush well to remove loose stuff; then give it a chemical clean. When you have flushed and rinsed the cleaner out refill using an inhibitor.

When you cut out the clogged tee, all the water from the F&E tank will gush out, so bale it out first. It may have sediment at the bottom, mop this out with a sponge to prevent it being washed down into the pump and rads.

 

[Arkwright]

Many thanks indeed, nickso & JohnD. I'll try that. So basically you're saying it's quite likely a pile of rust particles that have stuck together.
Thanks again.

 

[andsam]

If the position of the cold feed tee is difficult to get to you could try back filling through a drain point or open vent as a temp measure.

Andy