Why does my CH keep blocking up? (and how can I stop it?)

Over the last 3 months I seem to have found myself in an endless loop of flushing through my CH and then 2/3 weeks later everything is all blocked-up again, and I need to flush through again. -
To start with I found that a manual flush ( as in the wiki) worked but when this failed to work I took all my radiators off and flushed them through with a hose and also flushed through the primary heat xchanger. (I have a Baxi 105e combi boiler.) I got plenty of sludge out doing this. I filled the system up but 2 weeks later it was all blocked up again! This time I suspected that it was just the heat xchanger that was blocked, so only flushed this through, which worked fine. I also added some good quality inhibitor, but now, 3 weeks later, it has blocked up again.
Any ideas as to why this is happening, and more importantly how I can avoid flushing my CH every 2-3 weeks would be very useful.

Thanks in advance.

Martin

For god sake get someone in who knows what is happening and what they are doing.

You are just making the situation worse.

Washing out with water will not get all the sludge out.

Even power flushing doesn't get it all out.

Maybe you have just disturbed it and it is circulating round before settling again.

A Magnaclean is a clever device that attracts and holds circulating black sediment with a magnet (you can take it out and clean the accumulation off) so might be helpful. It will cost about £100 plus fitting. If you have not had inhibitor in from new then there is probably quite a bit of corrosion.

You could also give it a chemical clean which will take out more sediment than a water wash.

If you have to have a power flush this will cost hundreds of pounds.

If your system is drawing in new water, then it will never stop corroding. One cause is a leak.

Make sure your filling loop is actually disconnected and you are not losing pressure.

Thanks JohnD,
I figured when I was flushing my rads through that there must be a similar amount of sludge in the pipes which I was not really able to remove. My pipes are 10mm so probably wouldn't take too much to block. Having said that, it does seem to be the primary heat exchanger which is blocking the circulation. All the rads heat-up fully since I cleaned them through, and those closest to the boiler will heat up eventually through convection, even when the CH is blocked.
The Magnaclean does seem like a good option. I like the idea that I can remove any collections without having to keep draining the system (and hence having to buy more inhibitor)

I did omit that before the first time I flushed the system I had added a chemical cleaner. This should have been well washed away by now, but could well have dislodged any amount of rubbish. I have only been in this house for 3 years and this is the first year I have drained the system, so I cannot say whether it has always had inhibitor in.

Thanks for your suggestions.

Martin

The first thing you need to do is to clean the sludge out of your system properly. To do this you need to use a really effective cleaner. Look at the non-acid sludge dissolver on the link below:

www.aqueouslogic.co.uk

Put this in and circulate for a day or so. When you flush out make sure you flush each radiator individually and that all the TRV's, if you have any, are fully open when they should be. A lot of problems come simply from insufficient flushing.

This will remove the vast majority of sludge from your system and should resolve your problems.