The Strange Case Of The Banging Zone Valve

It’s “Mystery Week” in Blogville…we’re going to play detective to unravel The Strange Case of the Banging Zone Valve.  And in that spirit, our song of the week pays homage to all the great detectives — from Columbo, Banacek and Starsky  to Spenser, Magnum and Hutch — here’s Elvis Costello and “Watching the Detectives.”

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Now, on to our mystery!

Ed Taylor is a prime example of what a wholesale salesguy should be!  You could say Ed likes to think outside the box, but that would be selling him short.  No one ever told Ed there was a box, so he doesn’t waste time thinking in it.  Or around it.

Ed’s a freethinker and he comes up with some great ideas (ask him for his business card – you’ll get the idea). If Ed’s your salesman, you’re a lucky guy.

Anyway, Ed posted an interesting question on The Neighborhood a while ago, which led to a series of webinars and a new element to our training programs at Taco.  Here’s Ed’s story….

“OK all you wet heads out there; I need to tap into your vast wealth of knowledge. I work in a wholesale supply house and a customer of mine did a boiler change out. After the change out the homeowner complained about the heat pipes banging when the taco zone valves opened or closed, says the system did not do this before.


This is what the new system has:

Oil boiler ~ 90,000 btu, indirect water heater, all new #30 exp tank, feed valve, air scoop and vent, Taco 3 speed pump (00R). All 5 zone valves are existing, mix of gold and green heads and are spread thru out the basement on the supply side of system.


We did a road trip and sure enough the pipes banged when the zone valves opened or closed, but not all the time. We were able to make every zone do it over the hour we were playing with the system, we tried moving circulator from supply to return, was a little better but still banging, (original circ was Taco 110 and was on the return), system pressure is 12psi, we took exp tank down and checked 12psi (original tank was Amtrol #30)…..we changed tridicator during install because new one with boiler leaked (figures), so we have a new tridicator on boiler reads 12psi and does not move more than 1 psi during operation. We changed pump speed to low…no difference…boiler is cold start, high limit at 180 degree.

Ok…….somebody out there has had to run into this before ???????????”


As Sherlock Holmes would say, “Come Watson, the game is afoot!”

Let’s apply some Holmesian deductive reasoning to this mystery.  Clearly zone valves don’t just start banging because they feel like it.  Something has changed, so the thing to do is to start asking questions…

Do all five zone valves bang all the time?

If all five are calling and one closes, does it bang then?

Does the banging occur when only one or two zones are calling, and then one closes?

Ed replied by saying the banging only happened when one or two zones were calling.  When all five zones were calling, no bang.

Hmmm, a clue!

Let’s examine the evidence a little more closely.  There’s a new boiler, expansion tank, feed valve, scoop and vent.  In addition, they replaced a Taco 110 with a Taco 00R 3-speed circulator.  As we hydronic detectives like to say….



Let’s take a look at the pump curves for the Taco 110 (see it here) and the 00R 3-speed:

Taco Series 100 Pump Curves (click to enlarge)

Taco 00R/0010 3-Speed Pump Curves (click to enlarge)

As you can see, the 110 is a high flow, low head circulator, maxing out at just over 7 feet.  Compare that to the 00R 3-Speed, which is a lower flow, higher head circulator.  Both are circulators, but they are not the same.

Later, Ed reported the contractor replaced the 00R 3-Speed with a competitor’s 3-Speed.  No change…the zone valves still banged, even with the circulator at low speed.  Compare the Grundfos 15-58 3-Speed pump curve chart with the 00R 3-Speed:

Brand "X" Pump Curve Chart (click to enlarge)

Both are lower flow, higher head circulators.  These pumps are really designed for radiant floor heating applications, which by their very nature are lower flow, higher head applications.  You have 300’ lengths of ½” PEX, you have long supply and return runs to remote manifolds and you often have 3-way tempering or motorized mixing valves.  All of these add pressure loss to a system, pressure loss you wouldn’t normally see in a baseboard/zone valve job.

Bruce Marshall, trainer-extraordinaire for Emerson-Swan (Taco’s Manufacturer’s Rep for New England and Upstate New York) and one of the smartest guys I know (he has Patriots season tickets), suggested that Ed’s customer put in a Taco 007.  He did, and the banging went away.

Double Aha!

Here’s what happened:

The old Taco 110 was a flat curve circulator.  Let’s assume the total heating load on the job was around 80,000 BTUH, and that all five zones are equal in load, roughly 16,000 BTUH per zone.  If we use the Universal Hydronics Formula (one DANDY troubleshooting tool!), we can find the total flow rate for the job, and for each zone:

GPM = BTUH ÷ (Delta T × 500)


GPM = 80,000 ÷ (20 × 500)


GPM = 80,000 ÷ 10,000


GPM = 8


And for each zone:

GPM = 16,000 ÷ (20 × 500)


GPM = 16,000 ÷ 10,000


GPM = 1.6


Let’s take a look at those flow requirements on the Taco 110 performance curve chart:

Click to enlarge

At a flow of 8 GPM – all zone calling – the Taco 110 would create roughly 7 feet of pressure differential.  With only one zone calling – 1.6 GPM – the 110 was creating just a shade more pressure differential.  Essentially, there was no difference.

Now compare the Taco 00R 3-Speed, and the Grundfos 15-58 3-Speed:

Click to enlarge

Click to enlarge

With the 00R you see with all zone calling the head pressure at medium speed was just below 10 feet.  With only one zone calling, the head pressure jumped to nearly 17 feet.  The Grundfos produces less head that the Taco at those flow rates, but as you can see, there’s still a big difference when only one zone is calling.  And notice that even at low speeds there’s still a considerable amount of pressure differential being created when only one zone is calling.  The result?  Banging zone valves…

Elementary, my dear Watson!

Bruce suggested the 007, and he was spot-on!

Click to enlarge

With all zone calling, the head pressure was around 8 feet.  With only one zone calling the head pressure was less than 10 feet.   The banging zone valves have been silenced!

A couple of folks responded that a pressure differential bypass valve would have solved the problem.  That’s true, it would have.  But it would have also required some substantial system re-piping, as well as figuring out how to set it properly (luckily, we have a blog post on that! Find it here).  Pressure differential bypass valves are really band-aids in this case.  It’s an external fix to poor circulator selection.

The point is this:  there is no such thing as one circulator that works for every job.  When 3-Speeds first came out, the battle cry was that it was the only circulator you’d ever need, that it works for every job and makes circulator selection easy.  Well, as you can see in this example, it’s not and it doesn’t.  You’ve got to match the circulator to the job – pure and simple.

If it’s radiant, consider steeper curve (low flow, high head) circulators.  If it’s a baseboard/radiator job with zone valves (or zone pumping) consider flat curve (high flow, low head) circulators. Elementary!

What about variable speed circulators?  We’ll discuss those in the next installment.

Now for some questions…

1. Besides Ed, have you run into this situation out there in the real world?

2. How closely do you look at pump curves when putting together a job?

3. Who selects circulators for your jobs, and how?

4. Who was the better Sherlock: Basil Rathbone, Christopher Lee, Jeremy Brett (PBS) or Robert Downey, Jr?

I eagerly await your verdict!

2 Responses to “The Strange Case Of The Banging Zone Valve”

  1. Maybe if the cheap bastard who changed the boiler, had bothered to replace the aged zone valves with circulators there would be no banging. I have seen this exact problem when the cheap contractor, and the cheap homeowner decide eh we don’t have to change those, they work fine. Until the stupid valve tries to open or close causing the piping to shudder throughout the house. This whole problem does not come down to circulator selection, it comes down to cheap and lazy americans who if they could, leave the old engine that works good, into a new cadillac car to look good and run lousy. Replace the zone valve bodies stupid, and teach contractors and HO’s alike, don’t leave old junk to keep aggravating us good contractors to lose sleep at night fixing America’s cheap and lazy. Better yet, stop using zone valves and you won’t have these problems.

  2. Paul –

    I appreciate your input and your obvious passion for what you do and for our industry. Thank you for that! But I gotta ask, what are you so angry about?

    This was a pretty cut and dried case of misapplying a high head, steep curve circulator where a low head, flat curve circulator was required. With the appropriate circulator installed, the banging stopped. That’s just physics and science. New zone valves wouldn’t have made a difference either. Wrong pump, they’d still bang. Right pump, quiet as can be.

    And knowing the individuals involved as I do, neither lazy, cheap nor stupid applies.

    Thank for reading and thank you for commenting…it’s very much appreciated, and I look forward to hearing your take on things in future posts, We definitely need more passion like yours in our industry, and you’ve given me food for thought for future blog posts! I would ask everyone who posts here, however, to please keep a professional tone. We’re all in this together, and we’re all – myself especially – hoping to share and learn stuff here. I’d appreciate it!

    As my hero, the great Red Green would say, “I’m pullin’ for ya. We’re all in this together!”


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