8mm - 20 year old Central Heating System

[John]

Two radiators are getting sluggish. The last time I removed one for decorating I checked the flow - There was a good flow out of the "return" but a poor flow from the "flow" pipe.

The pipes are behind the plasterboard (wallpapered only last year) and in the case of the other - the pipes run under a laminate floor. I am therefore keen to try a cleaner - and was thinking that if I turn off all the other radiators it should maximise the effect on the blocked pipes.

Any comments - any suggestions? Do all cleaners need to be thoroughly flushed out? Are some better than others?. I have tried using mains water pressure to improve the flow - without success.

[cynic]

I have in the past rodded clear a similar pipe using curtain wire over about 4 metres

[Andy Hall]

I have a system of similar age and design. By the age, I suspect that yours is open vented as mine was. I had always been very particular about making sure that the system was regularly dosed with a good quality corrosion inhibitor such as Fernox or Sentinel (NOT the budget ones because they are questionnable and a false economy for an investment of several £k). I also took care to ensure that there was no pumping over or sucking down of air at the header tank. These are the main reasons as to why sludging happens in the first place.

The issue that I had was that the original installers had not done a very good job of initial flushing and there was quite a lot of copper swarf and other builders' crud in the system. This did tend to reduce flow in a few places although not severely.

I took the decision to replace the old boiler with a quality condensing model and to take the opportunity while doing so to give the system a very good flushing and cleaning. Part of this involved changing to a sealed system. Actually this is very easy to do and has a lot of benefits. Essentially, the header tank and vent are removed and a pressure vessel and filler arrangement are fitted. This could be in the same position as the old header tank, but I fitted mine in a void in the utility room where there is also a cold mains supply. Note that most new boilers will work with sealed systems, older ones may not

- that would need to be checked.

Having done the new plumbing arrangements for the vessel and filler and taken the header tank away, I fitted a strainer filter on the return pipe to the boiler and an isolating valve either side of the boiler.

I then took the radiators off, one at a time and out of doors for a thorough flush with a pressure washer. Care here because sludgy water stains indellibly. While a radiator was removed, I placed a hose adaptor onto the valve leading to a vessel and with what is now mains pressure applied opened the radiator valve to flush the pipework at each radiator and each valve in turn. This method has the advantages that there can be substantial pressure which will certainly clear out the rubbish and that it is taken out of the system altogether and not circulated round.

With the position of the boiler, it also meant that it was impossible for crud to be pushed through it - only clean water.

Once that was completed, the system was put back together and refilled. At that point a chemical cleaner is interesting to use because it will tend to mop up residual stuff. Heavy amounts of crud would not effectively be removed by chemical cleaner anyway, and residues etc are simply pumped around if you just put in cleaner and run it round the system without mechanical removal first. In any event, cleaners must be flushed out again.

The method proved very effective and on a repeat a few weeks ago, some three years after the original, the 20 year old system remains as clean as a whistle.

If you didn't want to go the whole hog of going for a sealed system, there is a way that you can still easily deliver mains pressure into it for cleaning and flushing. This would be to drain out the contents of the header tank and cut the feed pipe (the one at the bottom of the tank.).. Cut the mains supply one to the ball valve as well. Then remove the tank temporarily. Fit a stop end to the vent pipe that is over the top of the tank. Buy a filling loop as used for sealed systems. These are two valves, one being non return and a length of braided hose between them. Fit this between the mains and the feed pipe the right way round. When you want to flush at a radiator, open the valve there and then turn on the mains at the filling loop valve. Close and then repeat for each radiator position. At the end, remove the filling loop and reinstate the plumbing.