Flushed Away


Micron filters (this one is shown with a chemical pot feeder) should be removed prior to the cleaning procedure and replaced afterwards.

Cleaning, flushing, and preventing corrosion in closed-loop hydronic systems

By Roy Collver

Prior to his recent retirement from Plumbing and HVAC, Simon Blake suggested I comb through my archives for a topic that might worthy of revisiting.

He thought many of new faces in the industry would benefit, and that some of our technology has changed enough to make an update useful for the experienced hands. One of the first topics that came to mind when I looked at my back catalogue, was that of hydronic system water quality, specifically, how to clean and flush a closed-loop system and how to prevent them from becoming fouled by “stuff” in the first place.

Before considering any system clean and flush, information needs to be gathered. It is essential to partner with experts who can analyze the system in question and then help determine:

  1. What “stuff” needs to be cleaned out of a system;
  2. What should be going back into the system; and
  3. How to keep it clean after all of that work.

Local resources

Fortunately, there has been an expansion of resources available for those of us in hydronics. Local plumbing and heating wholesalers would be my first choice. They can steer you in the right direction either through their own in-house hydronics experts or by referring you to some of their suppliers who specialize in hydronic cleaning and treatment. I emphasize the word “local” when it comes to most things hydronic. Be wary of a good deal online. This is especially important with water treatment and chemicals of any kind. There are many local issues to be concerned with, from what stuff is in the local water to how local jurisdictions deal with disposal of cleaning chemicals, to what chemicals are even allowed (a big deal when the system has a domestic hot water tank or heat exchanger).

In Canada, there are some great suppliers with good representative networks, and most have a useful online presence. My shortlist includes manufacturers who have good wholesale distribution across the country, are friendly to the light commercial and residential contractor base and have a one-stop shopping product offering. I am highlighting these particular choices because they have easily accessed literature, technical support people and training materials that focus on helping you understand what you are doing and why, along with step-by-step “how to” instructions. There are many other suppliers and manufacturers in the Canadian market, and some of them are more regional. Do some searching on your own for the right fit—the best choice in your area may not be on this list.

Bob “Hot Rod” Rohr demonstrating the use of a Caleffi Hydroflush cart. (Photo: Caleffi)

Fernox Canada has been around for decades, and its products are highly recommended by many contractors. They have a whole suite of chemicals for cleaning and treating and a great power-flush machine as well.

One of my favourite suppliers is Axiom Industries from Saskatoon, who have a comprehensive product offering that has been carefully designed for ease of use by contractors big and small.

Another good resource is Caleffi. They have all kinds of specialty products, great training and literature resources and a very good representative network across Canada. They don’t supply chemical treatment, but proper use of their air and dirt separators can negate the need for treatment altogether. They also have a really good Flush and Fill cart.

What’s in the water?

Analyzing the fill water to be put into any new or old hydronic system is the first step. Municipalities should be able to give you an analysis of their treated water—otherwise, find a private lab. Chemical suppliers will often help you with this, or plug “water sample analysis lab” into your browser search and see what comes up for your area. Knowing what is in the water could influence some system design choices as far as component selection is concerned.

Do you need to demineralize, filter or otherwise treat the fill water? There are some nifty solutions for that, and manufacturers are making it easier. Find a demineralizing system that fits the type of work you do and use it for every system fill. In addition, are there other special fill water filtration needs? Is it wise to add on-going side-stream filtration, dirt separation, air separation or magnetic particle capture to help you keep the system in good shape?

A basic, new system start-up procedure should include: initial fill – clean and flush – refill and treat if required – not every system needs chemical treatment. Pay attention to the materials in your system to ensure treatment compatibility. Wetted materials could include copper, steel, cast iron, aluminum, brass a variety of plastic, fiber and rubber products, many of which might be damaged by using the wrong chemicals. From what I have read in the specification sheets for most of the newer residential/light commercial cleaners and treatment chemicals, there should be no issues with today’s common hydronic materials, and they should be compatible with common glycol solutions.

The dirty micron filter (left) was changed out after a clean and flush, while the cleaner one shows, removed six months later shows the clean and flush was successful.

Even if the water quality is excellent, new systems should be cleaned to remove any oil, pipe dope, construction debris and the like. Make sure you filter the fill water to avoid introducing particulates, even from treated municipal water. Micron filters should be removed prior to the cleaning procedure and replaced afterwards. Zone valves should be fully opened while cleaning and flushing—use manual shutoff valves, not zone valves to alternate flow between zones if desired.

After filling and air removal, cleaning chemicals are added to the system and circulated according to manufacturer’s instructions, then flushed out with plain filtered water until it runs clean. Blow-down any dirt separator and micron filter chambers, then completely drain.

The chemical people may tell you their products are non-toxic, but check with the municipality before you go ahead and dump the stuff into a sanitary drain. Never dump any type of chemical into a storm drain. For new and old systems, strainers, dirt and air separator coalescing media and other capture filters should be removed, cleaned and reinstalled after the flush-out.

Flush and fill

The key to successful cleaning, flushing and air removal is to create a high velocity fluid flow that will result in enough turbulence to vigorously scrub the walls of the system piping, boiler heat exchanger, heat terminal units and other components. This scrubbing action will help break up and remove encrustations, contaminants and sludge and keep them in suspension, so they can be expelled during the flushing procedure. System pumps are sized for a velocity in the four foot per second range, which is simply not fast enough to get a cleaning job done quickly. It is normal to take days or weeks of cleaner circulation, and even then, a lot of junk may still remain. A good way to make your life easier is to employ the use of a flush and fill machine. Check with your local wholesaler—they may have one they can lend or rent to you. If you do enough hydronic system work, you will likely want to purchase one.

An Axiom glycol feeder tank used to pressurize and fill hydronic systems without direct connection to potable water supply.

Existing systems are cleaned and treated using the same procedures as for a new system, but the cleaning cycle may have to be more aggressive and run longer. If components are really plugged up or corroded, harsher cleaning chemicals may be needed, and the procedure might need to be repeated one or more times. You may also have to pause the procedure and clean strainers and dirt separators numerous times to maintain the high flow velocities required. You should also diagnose what led to such poor conditions, so that you can recommend corrective action and preventative, ongoing maintenance procedures as well as determine what treatment chemicals should be added.

Not to scare you, but there is one precaution I highly recommend you adopt. In really badly-corroded systems, the cleaning process can remove enough material to damage some components and cause leaks—many leaks in some cases. It is important to let the client know that even though you will be very careful, leaks may occur. In these cases, it might be a good idea to have a liability waiver for them to sign.

To view past articles from Roy relating to this month’s column, visit www.plumbingandhvac.ca and click the links supplied in the article.

  1. Water Quality
  2. Cleaning up an old hydronic system
  3. Air Removal

My first article for the trade press was back in 1996. When the editor retired, Simon Blake took over the reins. Twenty-one years later, I call him a close friend.

He quickly got up to speed on the technical stuff I was writing about and asked the right questions. His rule right out of the gate—articles were to be manufacturer neutral—resulted in a highly regarded publication. 

He would give me few suggestions and we would arm-wrestle about how many words I was allowed. I am grateful to Simon for the way we collaborated to make my articles readable and visually interesting.

I am getting all choked-up submitting my 135th article to Simon (the article in this issue will be 136). I will miss the monthly banter but intend to keep in touch to see how his latest vintage motorcycle restorations are going and how well his newest model airplane flies.

His monthly editorials, with their calm and astute analysis of industry trends and influences, have helped shape a rapidly changing industry for the better.


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