Flushing frequency of central heating systems

AIUI, sludge comes from oxygen introduced into the pipes. Every time you change the water you introduce fresh oxygen. Therefore flushing is only something to do when the system is open for other reasons, eg repair work. Otherwise by flushing you're introducing oxygen which will then cause more sludge.

I don't think hard or soft water matters because the system should be closed and not regularly introducing more limescale into it. It would only be if you have a leak and the system is constantly topping up then would more water (and so more limescale) come in.

Theo

I have never flushed mine in 20 years. I didn't use any inhibitor either, though the boiler service man tipped some in after a partial drain down to replace a leaking valve.

In theory once the water has been de-gassed you shouldn't be adding more to the primary circuit anyway.

Of course, if you abolish private property, you also abolish the

If no one is responsible for society's assets, the country just gets poorer and poorer.

This is indeed the case. I vividly remember my ex's niece saying on leaving home 'I cant believe how much everything *costs*'. Never having been exposed to rent, rates, telephone bills, and so on.

People in 'social housing' simply don't care. Why should they - it's not their property.

This is my main beef about socialism and the state provision of anything. It transfers all responsibility from the person who can do something about it to a state that in general cannot.

It's a great idea. It just doesn't work.

A central heating system is a closed loop system. You are not replacing the water in it on a regular basis. If you have a leak of any kind you may start getting other problems as some water is being replaced.

If the central heating is not a sealed pressurised system and it has a loft top-up and overflow tank you could get a serious amount of sludge building up in your system if you have pump over. Pump over is where the hot water is pumped or forced up the overflow pipe into the open to atmosphere header tank. It could be because the pump speed being set too high. The result is oxygenated water is now circulating in the CH system.

You may need to flush it if an inhibitor hasn't been used from day 1. Sludge/rust will build up in the bottom of radiators and if fitting a new boiler to an older system it's almost mandatory for power flush for the boiler guarantee. Modern boilers tend to have narrower water paths that can block more easily.

In my opinion, even without a new boiler it's worth fitting a magnetic filter in the system. Again for a new (gas) boiler it's recommended and a condition of the guarantee that such a filter is fitted in the return path to the boiler. When I first fitted one to an older system it caught a lot of material in a very short time. Probably the act of draining and refilling disturbs a lot of material that normally sinks to the bottom of radiators.

From my experience a chemical cleaner didn't do much for my 20 year old system - when draining the water ran fairly clear. The subsequent power flush prior to a new boiler did remove a some sludge but I was told by the person doing the flush that my system appeared to be clean compared to many he had seen.

As for the cleaner anything that Screwfix/Toolstation sell would do the job.

As for inhibitor anything that screwfix/toolstation sell will do the job. I've usually gone for the cheapest screwfix/toolstation product after draining down the system. I've only ever drained the system for maintenance such as replacing a pump and where the isolating valve had completely seized or changing a downstairs radiator for something larger.

Hard or soft water *should* not really have any impact - you are only adding water to a system infrequently if it is working properly. However it can be a problem on systems that are needing frequent water top ups.

A system will only *need* flushing in some circumstances:

Typically when just installed or when significant alterations have been made and you need to remove things like metal particles, flux residue, loose solder etc.

When performance is being affected by sludge build up - like blockages, rads that won't heat or only heat at the top etc. A boiler that is "kettling" due to obstructions or scale in the main heat exchanger.

Also when a boiler is replaced - especially with modern high efficiency boilers that tend to have primary heat exchangers with more numerous narrow water paths.

Vented systems are more likely to suffer than sealed ones since it is easier for oxygen to enter the water.

Modern systems are often fitted with filtration devices designed to capture sludge and other debris - these also reduce the need for full on flushes.

I last flushed my system about 14 years ago when I changed the boiler. Since then I have cleaned the filter from time to time, and added inhibitor periodically. So far the water remains relatively clean.

Any of the well known brands (Fernox, Sentinel) etc. Generally unless cleaning a system in poor state you won't need a cleaner, just make sure there is enough inhibitor to keep corrosion (mostly) under control. (you can't fully eliminate corrosion - some will be galvanic and not dependant on dissolved oxygen)

More details on flushing here:

David snipped-for-privacy@nospam.com wrote in news:viel87$1khp5$ snipped-for-privacy@dont-email.me:

I don't feel the need for regular flushing but I do have a magnetic/cyclonic filter fitted on the boiler return to catch any nasties. I've just replaced the expansion vessel and so have been doing some draining and have topped up with half litre of inhibitor concentrate which neatly fits in the volume of the filter once drained. A recent cleanout of the filter (first in 2 yrs and easily done) showed a bit of magnetic sedement/fragments which otherwise could have been blocking up my heat exchanger.

Examples: Filters:

Inhibitor:

Thanks for the replies.

I currently doing a cleaning session on my CH which is an open vented system.

For some reason it has always seemed to be very prone to sludge build-up. The last time I had to do a clean was about 2-1/2 years ago. I know when it needs a clean when the boiler starts kettling.

I have always used the Fernox range of treatments. I once tried another brand which didn't work very well. The Fernox cleaner I now use is the F3 and after flushing the system as per the recommended procedure by Fernox, I use the F1 inhibitor to try and stop corrosion etc.

From the replies, it seems that a CH system shouldn't need such frequent cleaning hence my original question.

I see Fernox do sell an biocide F7 which seems to be intended for systems other than CH systems, but I'm wondering if this may be a worthwhile investment.

Thanks for the link.

I'm wondering if the sludge is microbiological.

I usually find the header tank is full of sludge, or probably more correctly, slime. I always hand empty the header tank before I start the drain-down to stop the sludge/slime from entering the system.

After draining down, I add the F3 cleaner to the header tank before refilling the system. The kettling stops after refilling which means that the F3 cleaner can't have had time to do it work.

I'm wondering if the sludge/slime is blocking part of the system, and simply draining down is enough to dislodge it and ensure free flow is restored.

Consider converting it to a sealed system. Lots of advantages and few disadvantages.

Tim

That may be a worthwile exercise. However the wiki.diyfaq link does say that microbiological contamination, if that is what I have, can exist in closed systems.

Have you checked that it is not "pumping over" - i.e. discharging water via the vent pipe into the CH expansion tank? That causes lots of fresh oxygen to be pushed into the water and will give accelerated sludge build up.

Only if you are getting lots of lots of organic or fungal growth in the header tank.

It can exist in a sealed system, but would be very rare. Once treated and got shot of, ought not come back unless there is fresh O2 getting back into the water.

No its not pumping over.

It is. If it is an anerobic bacteria or fungus then it can survive without oxygen, so a biocide is probably the only way to deal with it.

When our new boiler was installed in early summer, replacing an 18yr old boiler, the engineer reworked the pipes and installed an Inlet and Outlet to bypass the boiler for flushing. He then spent a whole day powerfushing each radiator with a cleaner added to one of the pumps and a big magnetite filter to the other (I think that was the arrangement, in series). He's flush until the filter was clean before moving on to the next radiator. Some were dirtier than others and certainly my study radiator, which was particularly obstinate on the flush, now gives off more heat.

An acquaintance who had a new boiler a couple of months earlier only had a chemical flush utilising the new boiler's pump. I did ask that installer for a quote, which he gave, but then didn't seem to want to talk to me when I pressed him on his pre-install procedure.

I suspect I got a better job at a lower price and don't expect to need any more flushing at least for the life of the boiler and more.

I doubt that the initial install, or boiler replace, was done with such care.

Would this be a problem if the header tank overflow is dripping for a long time? ie header tank is full because the ball valve isn't sealing properly, heating comes on, water expands, pushes some water out of the overflow. Heating goes off, water contracts, ball valve fills up gap in the header tank with fresh oxygenated water. Rinse and repeat.

Or is the water in the system somehow disconnected in normal operation so any oxygen in the header isn't diffusing into the heating loop, or the rate of diffusion is very low?

Theo

When I had my boiler replaced it was also moved to a better location. My power flush was to the feed and return pipes bypassing the boiler which at time was fitted but not commissioned.

My flush of 7 radiators took around 3 hours.

The equipment used on my system had its own pump and two industrial size magnetic and mesh filters. All radiators except one were turned off at the lockshield valves. Water was pumped through the one radiator and the direction of flow repeatedly changed. During this procedure the radiator was hit with a rubber mallet* to dislodge the sludge in the bottom of it. Once the return water ran clear at the flushing machine the next radiator was flushed.

Cowboy installer :) especially if fitting a boiler to a old ch system.

On my quote for the boiler replacement the itemised price for the power flush was around £350. This was a couple of years back. My mother had a quote for a power flush and was quoted £800 by BG. She had it done by a small local company for around the same price that I paid.

• I mentioned to the person performing the flush that I had seen videos of the radiator being vibrated with a rubber attachment on a SDS drill. The response was with these attachments you soon find out of if the radiator brackets are firmly attached to the wall or just hanging on for dear life in crumbly old plaster :)

Anaerobic bacteria need *something* to feed on.

There isn't much in the way of nutrients in modern tap water so in a sealed system they should not proliferate.

In an open system aerobic is simply more likely.