Blocked cold feed and leak

Hi, I recently moved house and a few days ago my central heating broke down. Even since I moved in the system was quite noisy, but it had been getting louder over the last few weeks until two days ago when it would start up but after the boiler had fired up it would cut out after more than only a few seconds use. The sound coming from the pipework (around the cold feed and vent pipe) when the boiler fired up was somewhere between someone hitting the pipework with a large hammer and someone successfully sucking an egg through a small hosepipe.

I believed the problem to be either an air lock or a blockage around the cold feed. I tried a magnet around the suspect pipework and it stuck well, so I tried to remove the pump to access this. Unfortunately the pump valves had seized and were weeping so I partially drained down the system and removed the pump to be able to clear the blockage. There wasn't a significant amount of crap in the pipework though, and although there was a little in the F&E tank it was settled below the level of the cold feed pipe and so I thought a blockage was unlikely to be the cause of the issue.

So I thought it was probably due to an air lock as there are quite a lot of horizontal pipes in the loft. I refitted the pump and tested the pipework for leaks. Unfortunately there was a leak (I think I must have bent the pipework in the process and/or the pipework was really old and had corroded).

So now I'm left with two problems I could do with some advice from some plumbing gurus for:
1. Is there any likelihood that it might be possible to repair this without having to replace the pipework?
2. Does it take much to block the cold feed? Because I could reach all the areas of piping the magnet stuck to with a bent hanger without a problem, yet the amount I managed to remove was quite pitiful…

My boiler is a glow worm fuelsaver and the pump is a grundfos if this is of any use.

Thanks!

I once had a problem with my own system that had a myson air separator in an arrangement like yours.

I was able to take it out (yes that means cutting some of the pipes) check it and find it totally choked up (in the separator), clean it out refit it and all back to normal again. That was a long time ago, today I might be tempted to use a flushing agent first!

In your case simply get a new separator e.g
http://www.heatingcontrolsonline.co...d-p-269.html?gclid=CLzCqbm58rsCFQXLtAodlV0ATg

Hi,

I would strongly suggest replacing the airjec. The only way you'll shift that blocked cold feed is to mechanically break it up with something like a coat hanger. This would move the blockage elsewhere, which would be bad news for your system.

Chemically cleaning won't shift it if it's completely blocked. Cold feeds regularly block like this so don't take it personally

Changing the airjec is a simple ish job.

Hi, thanks for your helpful responses, I've ordered in a new air separator and plan to replace it - probably storing up trouble for myself otherwise as you say. I was a little confused why the magnet wouldn't stick around the air separator inlet if it was blocked, which I think it must be, but I suppose a magnet might not be the ultimate conclusive test. Thanks guys.

The reason the magnet sticks is because the sludge is actually iron oxide also known as magnetite.

Your magnet won't stick to the copper but it will stick to the iron oxide. A big deposit would show with a magnet.

The deposits in the blockage could also be non magnetic.could be scale, bio-slime from the tank or other contaminants.

I've replaced the air separator but (unfortunately?) it was actually in pretty good nick magnetite-wise. So sadly I still have the situation where the boiler starts up fine but quickly boiling water flows over into the F&E tank through the vent and it sounds as though air is possibly simultaneously being sucked down the cold feed(!?). If it helps I should add this happens when trying both the central heating and hot water. I've posted a video on youtube if this is helpful to explain: http://www.youtube.com/watch?v=Ng24TxNvAeM&feature=youtu.be

I suspected from all this the problem must be a blockage. But the water comes out of the drain point and bleed valves crystal clear… I've been all around with a magnet and can't find any pipes or radiators that are blocked using this method, so if I need to cut any pipes out I'm not sure where I should do apart from probably within the general boiler cupboard area. In desperation I drained, dosed the system with sentinel X800, and refilled but this didn't manage to shift anything. It did say if there is a blockage it wouldn't work though, but as I say, desperate measures... I did measure the amount of time it took for the boiler to cut out to see if this increased as the x800 went to work - it did a little from around 20 seconds to 30 seconds, but that was it and I think I'm clutching at straws at any sign of hope to be honest!

If you have any ideas what might be causing this then it would be great if you could help and much appreciated. I'm quickly approaching get-the-pros-in time but I thought one more try on here probably wouldn't hurt, who knows, you might have had exactly the same thing before!

Do you know if the pump is actually running?

I could not find the manual online so copied mine - Click image to enlarge and read! If it is running OK I would recommend bringing in a heating engineer.

change the pump

Thanks for copying that Blagard, I struggled to find the manual too. Yes looks like it was the pump that had gone after all. When I start it manually it works great. Wish I'd properly tried this first time... I thought it was working as I could feel it vibrate and rumble when it was on, the shaft wasn't seized and plus I thought the hammer to the side would do the trick if anything. Thanks guys.

Whatever you do don't install the pump as it is...the shaft should be horizontal.

Gasguru said:

Whatever you do don't install the pump as it is...the shaft should be horizontal.

Click to expand...

Drat I missed that!

Copy from the manual for the OP to show the options. Noting the four positions with a big X through them to show them as not acceptable.

I bought a new pump today (installed so the shaft is horizontal, thanks for the heads up) and it's working like a dream, significantly less noisy than the old pump. So all sorted now, thanks again!