Cleaning, flushing and treating hydronic systems By Roy Collver
Although not an expert in this topic, I have been observing over the years what seems to work and what doesn’t. I have listened to many “experts” and I think I have a pretty good handle on it. Cleaning out and treating a hydronic system is an important, but often forgotten, step in protecting system components and maximizing efficiency. The two different reasons to perform these procedures each require a slightly different approach. New systems: When a new system is installed, it should be flushed to remove any debris, solder flux, pipe dope, oil, etc. This step should never be skipped, and the stories are many when it comes to the kind of stuff found in some brand-new systems. I personally have dug twigs and leaves out of a “Y” strainer, wood splinters out of pump impellers, and once – a glass marble out of an air separator. I have seen strange gel plugging a basket strainer, and dealt with noisy boilers due to oil and grease coating water-side heat exchanger surfaces – all in brand-new systems. If an installer has taken reasonable precautions to be sure there are no big
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Ops Talk • Fall 2012
chunks in the new piping and to be sure that there is no solder flux or oil in there, they might lobby to get by with a clean water flush and dump of the system – don’t buy it. Get your mechanical engineer or facilities manager to specify that the installer engage with a firm that is an acknowledged local expert in hydronic fluid treatment and system cleaning. These people will assess the system and water quality, and prescribe a cleaning and treatment regime appropriate to the materials in your system and appropriate to the condition of the local water. They should be capable of ongoing testing of the system, and have a “suite” of chemicals that will be compatible with each other and not gum up the works. This all applies to new systems and retrofit situations when boilers and other major components are replaced. Old systems: You should also clean and flush when an older system gets fouled by sludge, rust/lime scale, algae, etc. There are all kinds of nasty things that can show up, including exhausted chemicals and glycol that has “gone bad” (usually faded down into an acidic state – very hazardous to your system). Part of a regular
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maintenance check should be to drain fluid samples and check pH and chemical inhibitors. Should there be any chemicals in the system, you will need to know what they are; if need be, farm the job out to your supplier who will be unlikely to cause any “mix’n’match” problems. Some chemical suppliers will provide you with a test kit to go along with the chemicals you buy from them so that you can do this yourself. This detail is important and should be a key decision point in deciding which chemical supplier to work with. Equally good are the suppliers that have a lab with quick turnaround, where you can send a sample for testing. Other ways to determine if a system needs to be cleaned include draining some water from low spots in the system if any are accessible, and looking at what comes out. Depending on the materials of your system, the fluid may be coloured – and this is not always a bad sign – but there should never be any grit that comes out. I am a great believer in “Y” strainers and cartridge filters, and the newest dirt separators are brilliant. All of these devices will help capture junk in your system, but just as crucial,
