Plastic Microbore Sludge Problem

4 Oct 2010
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United Kingdom
I moved to a 10 year old detached house about 18months ago which I later found out was on an estate well known for heating problems caused by sludge formation in the system. Having survived a harsh winter, I think our system is not too bad at the moment –except that the two lounge radiators and the bathroom radiator have large sludge deposits in the bottom which greatly affect the heat output.

The heating system is 10mm microbore and has a new Worcester Combi-Condensing boiler fitted. I have learnt from my neighbours that the main part of the system is made up of plastic microbore pipework but that there are no manifolds -although I find this hard to believe. Apparently the 10mm copper coming out of the wall only makes up a small part of the system.

My neighbour says that the system was pressure flushed on at least two occasions by the previous owners, but I think I can expect the sludge problem in radiators to get as bad as some of the other houses on the estate in a short time!

I have successfully installed two towel rail radiators and had planned to just replace the problem radiators in the lounge (fitting TRV’s at the same time) before filling up the system and adding inhibitor.
But I would like to know:-
a) Are there any ways that the “sludging up” of the system could be stopped?
b) Is there any sort of electrolysis going on due to the radiators not being connected by copper pipe?
c) Would my best course of action be to add Sentinel X400 to the system for about 4 weeks, drain the system, flush the system, replace the lounge radiators and refill the system together with Sentinel X100 or Fernox inhibitor?
d) Assuming the house radiators fitted were of the ‘cheap and cheerful’ type, are there any better quality ones on the market that would resist rusting?
e) Is Sentinel safe to use on plastic pipes?

Lots of questions. Any answers please? :confused:
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I would want to see the sludge to get an idea of what its caused by.

Are you sure the plastic is barrier pipe? Usually says on it. If not there thats the likely problem.

X400 for four weeks is easy for you to do and will help I expect.

But I would use something more agressive like citric acid ( DS40 ) but that has to be used with care.

Before being more specific I would want to know the underlying cause of the problem.

Thanks Agile.
I will try to take a photo of it when I next drain down.

How do I recognise barrier pipe, just by writing on the side? What is special about it?
If you look at a cut end of barrier pipe, it has a thin later in the middle, which is pretty obvious.

If you have "tea leaves" of black stuff collecting, that can be characteristic of barrier pipe. Black sludge can be anything, red rust colour means recent serious oxidation.
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The molecules of air are small and light and can penetrate through normal plastic pipe and the oxygen rusts the inside of the rads.

Inhibitor can help but will not prevent serious problems with non-barrier pipe.

The extra layer somehow stops the air getting through the pipe and should always be used for heating systems but its more expensive!

Plumbers installing for builders rarely clean or inhibit their heating systems so they start off badly. Since cleaning properly is quite expensive owners dont want to spend whats needed to fully clean and inhibit and just change the pump every year as it wears out.

Ask a few neighbours. There may be a local plumber who has been to all/most and knows the problems well.

Thanks ChrisR and Agile.
So, given the system which I have inherited and the probability that I won't be replacing miles of plastic pipes in a hurry, do I:-

a) add Sentinel X400 to the system for about 4 weeks, drain the system, flush the system, replace the lounge radiators and refill the system together with Sentinel X100 or Fernox inhibitor and be prepared to do this each year?
b) consider a power flush if things get bad?

Also, are there any better quality radiators on the market which may resist corrosion -or is this just a waste of money?


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