A Properly Designed Hot Water Heating System

Some systems will have many valves and some will be very simple single zone systems

A nicely piped hot water heating system
Credit: dreamaker

Basic Hot Water Heating 101

What you need to know before you can fix the problems

Hot water heating systems are widely used to heat homes and business' around the world. They are also used to heat driveways and pools, domestic hot water and slabs of concrete. Whatever the system design you're dealing with; if it's a hot water heating system than it should be free from unwanted air.

Hot water heating systems today are designed to work under pressure. They run between 12 and 25 pounds per square inch and this pressure is created when the system is initially filled using city water pressure or the pressure created from a well pump.

When any heating system of this type is installed and put into service, the installer will purge the air out of the system by pushing city water; or well water through the loops and out a garden hose. The plan being to also push out unwanted air until the system is 100 percent filled with liquid. 

Once we have removed all the air by purging; the system is designed to keep up that 12 to 25 pound pressure setting. This is accomplished with the use of an inline valve called an auto feeder. This will be installed somewhere between the source of water you fill your system with; and the boiler and piping of the heating system itself.

As long as the entire system remains unde pressure, it's very difficult for air to be introduced to the system. There are however several ways that it can happen. One way for air to get into the piping is for the thermal expansion tank to blow its rubber diaphragm. These tanks are pre-charged with air to allow for thermal expansion within the system as the boiler heats the water. 

When the thermal expansion tank fails on a hot water heating system; the air in the tank passes through the blown rubber diaphragm and enters the piping. It mixes with the system water and that's the noise you'll hear that resembles the sound of a river running through your home.

To get rid of the noise as well as keep up the proper operation and avoid a no heat situation, the air must be removed from the entire system. Of course in the case of a blown tank you'll need to replace the thermal expansion tank; before purging the air from the system. 

Another common way for air to infiltrate a hot water heating system is when a leak developes on the suction side of any circulator pump. Whenever a thermostat calls and starts the pump for that zone; it can suck a small amount of air into the system when the pump starts. The leak may not even be big enough for water to show and it also may only leak when the pipes are cold. This happens because the threaded fittings and flanges tend to expand when the system heats up and this will stop the leaks. They will usually come back when the system cools.

To diagnose leaks at the pump flanges; allow the system to cool completely. Any leaks will become clear when the metal contracts to its normal size.

Repairing this second problem consists of tightening flange bolts, or possibly replacing any bad gaskets. The repairs must be made, and then the system must be completely purged to eliminate any air within the piping and boiler. 

Taco Circulator Pumps

The most common hot water heating pumps on the market today

Taco 007-F5 Cast Iron Circulator, 1/25 HP
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(price as of Oct 28, 2016)
These pumps are very reliable and easy to change. four bolts and two wires and the whole pump is brand new. Amazon will ship them right to your door and gaskets are also available through this link.

A Simple Single Zone Hot Water Heating System

Locating the purge setup

A single zone hot water heating system.
Credit: dreamaker

This is a single zone hot water heating system. The purge setup is in the return line on the right side of the picture. The ball valve is down low and the boiler drain is up high. This combination may be closer together or far apart like they are here on this system.

Manifolds are used for Multi-Zone Systems

8-Branch Brass PEX Manifold Set for Radiant Heating, 1/2 PEX Adapters
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(price as of Oct 28, 2016)
Using a manifold to pipe a multi-zone hot water heating system is the easiest way to configure the piping.

Finding the Purge Set-up on a Hot Water Heating System

Locating the purge set-up on any hot water heating system will be a lot easier if you know what you're looking for. 

Purge set-ups consist of two valves. One valve is a positive shutoff ball valve or other type of stop. The second valve will be a boiler drain and should be somewhere near the ball valve in the same pipe. This duo of valves will usually be repeated for each zone or loop in the heating system.

If you stand in front of the boiler and look at the piping you'll see one large pipe exiting the top of the boiler and one large pipe entering the bottom of the boiler. These two pipes will either reduce in size as they go away from the boiler or, they'll split into multiple zones or loops. 

Some systems are only one zone. This single zone system will have only one purge set-up. It will usually be found in the return line of the loop as it comes back from the zone.

Direction of flow can be detected by looking on the body of the circulator pump. There will be an arrow telling you which way the water is flowing. Before the water goes back into the boiler is the best place for a purge set-up but some installers will put them just about anywhere in the loop.

Check out the picture I've included of a simple single zone purge set-up; one ball valve and one boiler drain.

Next check out this multi zone system with many purge set-ups. Notice the alignment of all the pipes and valves. The installer of this system cared about what people thought of the work. Some folks won't be as fortunate and the system you may be dealing with could have purge set-ups scattered around the piping.

You'll need to find all the purge set-ups and figure out where all the pipes go. Understanding the heating system's direction of flow as well as which feed line connects to which return line; is imperative to getting a proper purge and solving the air problems.

Honeywell Zone Valves

Simple reliability

Honeywell V8043F1036 3/4-Inch Sweat Zone Valve with Screw Terminals and End Switch
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(price as of Oct 28, 2016)
Honeywell zone valves have long been the preferred valve with contractors and homeowners alike.

Other Components Involved in the Purging Process

Once we know were all of the purge setups are located we must also locate and understand how the automatic feed valve works. This is a valve that you'll find installed in-line in your water feed line. That's the line that fills the system. It will come from your city water lines or the well pump supplying domestic water and it will tie into the boiler piping to add water to your heating system. Somewhere along the way; usually close to the boiler for easy access; you'll find the automatic feeder valve.

Auto feeders come in different styles. Some will be brass and have a purge lever on top. Some will be made from cast iron and they may have a screw type stem that winds down to increase the pressure setting. Both types of valves play a crucial part in the proper procedure to purge any hot water heating system. Identify the valve and make sure you understand how your particular model functions.

If you have the lever style valve; you'll be lifting the brass purge lever straight up during the purge process. This allows the water to flow faster and with more pressure to help push out all of the air.

The screw stem style automatic feeder valves need to be either wound up or wound down to increase the pressure they allow through, to get high enough to get the air out.

To figure out which way yours goes; you'll have to turn it in a little and see if you hear the water line filling the boiler. If nothing happens, turn it the other way just until you hear the water flowing in. The pressure gauge on the boiler should rise slightly as well. Once you've figured out how to make the valve increase the pressure, put it back approximatly where it was until we're ready to go.

There are a couple of more components you'll have to deal with for a proper purge. These will include any automatic air vents that you have installed in the system. They are small brass or chrome vents installed on top of; or near the boiler. They're designed to remove any small micro bubbles that are left in the system after the purge is completed.

These auto vents work with a float system inside and get clogged up very easily. For this reason it's important to always close the little caps on the auto vents during the purging process to avoid any foriegn particles from getting stuck in the auto vents. Just close the caps hand tight.

Another system component that must be adjusted for a proper purge will only be found in multiple zone hot water heating systems and sytems with indirect domestic hot water zones. This valve is called a flow check.

Flow checks are installed to stop a natural gravity circulation from occurring as the boiler heats the water. That causes zones that are not calling to over heat. A weight inside the flow check valve prevents this gravity flow. It can also hinder the good flow were looking for from our purging efforts.

There will be one of these valves installed in-line for each zone; usually in the feed header as it leaves the boiler. To adjust this valve for a proper purge; open the stem or stems all the way up. This will lift the weight inside so a good flow can be achieved. 

The last component that you must be concerned with are any zone valves the system may have. These arte electrical valves that are installed in-line in each loop of a multiple zone system. Not all multi-zone systems will have zone valves. Some will use a circulator pump for each zone. This illiminates the need for zone valves.

If you have a zone valve system; the zone valves will all need to be manually opened for the purging process. Do not manually open any zone valve until you have shut off all the power to the heating system. This will burn out the valves. Once the power is off; use the manual lever on the zone valve to hold the valve open.


Spiro-Vents; Auto Vents on Steroids

For major air elimination issues

Spirotherm VJR125
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(price as of Oct 28, 2016)
Some hot water heating systems will have issues with air due to their size or configuration. A Spiro-Vent can help with excessive air problems.

Purging a Hot Water Heating System Step by Step

Eliminating air by the numbers

  1. Shut off all power to the heating system. This can be done at the boiler emergency switch; or the house electrical panel. 
  2. Allow the system to completely cool down. This may take several hours.
  3. Connect a garden hose to the boiler drain for the longest zone in the system. We'll work back to the shortest zone.
  4. Run the hose outside where it can safely discharge without damaging anything.
  5. Place the end of the hose in an empty five gallon bucket.
  6. Close the ball valve for the purge setup on the zone your working on.
  7. Check the pressure on the boiler pressure gauge. Make a note of where it's sitting because this is the normal pressure and we need to put it back there when we're done.
  8. Close the caps on all the auto vents installed in the system.
  9. Open all the flow checks installed in the system.
  10. Manually open and lock all zone valves installed in the system.
  11. Open the boiler drain for the zone your connected to. Water should begin to flow out of the hose.
  12. Check the pressure on the boiler gauge. It needs to be running at twenty-five pounds; or as close as you can get to that to properly push all the air through the loops and out the drain. To get this pressure you may have to open the auto feeder valves purge lever by lifting it straight up; or increase the pressure by winding in the stem if you have that type.
  13. Use caution when opening the auto feeder to keep the pressure from rising above twenty-five pounds. If it does exceed 25 pounds you will set off the pressure relief valve. Those are set to go off at thirty pounds. You may have to throttle down the pressure with a shutoff valve which should be found in the fill line close to the auto feeder. This can be partly closed as the waters purging to get the desired 25 pounds of pressure for an ideal purge. If the pressure is still lower than twenty-five pounds when the auto feed valve is opened; you can throttle down the drain valve until the pressure gets to twenty-five pounds and runs there consistently.
  14. After obtaining a constant pressure of twenty-five pounds by adjusting the feed valve and the drain valve for the zone; go outside and observe the water filling the bucket. Check for air bubbles escaping and run the purge until they're no longer present. This can take anywhere from five minutes to an hour or more; depending on the amount of air in the system; how consistent the pressure is during the purge; and the configuration of the zone. Longer zones will take longer to purge and shorter zones will be quicker. When the zone is completely air free there is a process to shutting down the purging operation that must also be followed step by step. Doing it in the wrong order will create too much pressure within the system and blow off the pressure relief. 
  15. Close the auto feeder valve lever; or reduce the feeder pressure with the stem before closing the boiler drain in the purge setup. This resets the auto feeder valve to the normal operating range of 12 to 25 pounds. This should be the same as the pressure was when you began.
  16. Close the purge setup boiler drain.
  17. Move the hose to the next zone if you have a multiple zone system and repeat the above steps.

Do the same with each zone in the system. Work from the longest zone to the shortest zone until all zones in the system have been completely purged. The next section will walk you step by step through putting the system back into operation and checking out your work.

Thermal Expansion Tanks

A blown tank can be the cause of air in a heating system of this type

AMTROL EX-15 15 Extrol Expansion Tank
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(price as of Oct 28, 2016)

Putting the Hot Water Heating System Back Into Operation After Purging

Step by Step

After the purging process has been completed on all zones within a hot water heating system; the next step is to bring the system back on-line. The following list is a step by step guide to getting everything back up and running post purge.

  1. Remove the garden hose from the last zone and check all boiler drains for drips. Caps with a garden hose washer can be purchased to fix a dripping valve temporarily.
  2. Open the ball valves in all the purge setups. (Do this slowly so the pressure can equalize)
  3. Close down any flow check stems that were opened by winding down the stems in a clockwise rotation until they seat. Check the packing nut on the stems for leaks; they may need to be tightened a half turn to stop any minor leaks.
  4. Make sure the shut-off in the water feed line to the system is all the way open and check the gauge on the boiler. It should read the same as it did before you began. (Somewhere between 12 and twenty-five pounds).
  5. Open the caps on any auto vents that were closed.
  6. Turn all thermostats down to their lowest setting.
  7. Turn the power back on to the system.
  8. Raise one thermostat to make the system call for heat.
  9. Listen carefully as the system fires and any pumps come on. You will hear small amounts of noise on the first startup and this can continue for several minutes. Allow the water to circulate for five or ten minutes and then take note of any noise. If the purge was successful, your heating system should be free of noisy flowing water sounds.
  10. Recheck the boiler gauge after the boiler is up to temperature. This means the temp has reached high limit and shut down the burner. Be sure to observe an entire heating cycle until everything shuts off properly.
  11. Put away your tools you have successfully eliminated the air in a noisy forced hot water baseboard heating system by purging the system.


Get the Air Out

For systems that sound like a river

Fix My Noisy Hot Water Heating System How to Eliminate air from a hot water heating system
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(price as of Oct 28, 2016)
If you have air in your hot water heating system, it will sound like a river running through your baseboard. Getting the air out is not easy unless you know how. This book will teach you how.

Repair your own Heating System

Save a pile of cash on minor repairs

Repairing Hot Water Heating Systems
Amazon Price: Buy Now
(price as of Oct 28, 2016)
Service calls can run into the thousands of dollars. Most people have the ability to do many repairs themselves. This book will help those people along.

Get in the Know

Learn the components that make your heating work

Understanding Hot Water Heating Systems
Amazon Price: Buy Now
(price as of Oct 28, 2016)
Even if you never work on your heating system, it helps to know a bit about it. You'll be much better prepared to discuss the issues and negotiate the price for repairs.

When You Want the Best

Stainless Steel Answers the Call

Taco 007-SF5 Cartridge Circulator Stainless Steel
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(price as of Oct 28, 2016)
When nothing but the best pump with the absolute top spot for longevity, this is the Taco circulator pump you'll want.