Leaking heating circulator pump at the mounting flange (C) Daniel FriedmanLeaks at Heating Circulator Pumps
Where do leaks occur at zone circulators, why we care, how to fix them? When is emergency repair needed?

  • CIRCULATOR PUMP LEAKS - CONTENTS: Leaks at heating boiler circulator pumps - where and why they occur. Circulator Pumps: Hot Water Heating System Circulator Troubleshooting & Repair Guide. Circulator pump relay switches & controls on heating systems: Troubleshooting & Repair. Video of a rapid leak at a circulator pump.
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Circulator pump assembly leaks on hot water heating systems:

Here we explain how to find and fix the common points of leakage found at heating system circulator pump assemblies.

This article series discusses Circulator Pumps: how to find, inspect, diagnose, and repair problems with Hot Water Heating System Circulator Pumps or circulator pump relay switches and controls. This article series answers most questions about Heating System Boiler Controls on central heating systems to aid in troubleshooting, inspection, diagnosis, and repairs.

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Leaks at heating circulator pumps: where leaks most often occur (circulator pump mounting flanges)

Leaking heating circulator pump at the mounting flange (C) Daniel Friedman

Article Contents

Small Leaks at a Circulator Pump - Mounting Flange Gasket Failure

A common spot where we find leaks on hot water heating systems (hydronic heating) is at the flanges mounting the circulator pump to the heating water distribution piping. Notice the white salt deposits on the circulator pump in our photo?

Note that the white deposits can be followed upwards to the upper circulator pump mounting flange bolt. More stains suggest leaks are active at the lower flange too.

[Click to enlarge any image]

Perhaps this is due to a failure to properly tighten the mounting bolts, or possibly because the flanges are supporting quite a bit of weight when larger (B&G type) circulator pumps are installed rather than the smaller (Taco type) pumps.

Because the heating distribution piping is normally hot you usually won't see water on the floor very often when there is a leak at the circulator pump mounting flange - only in extreme cases.

But if the circulator pump is leaking at the flange mounts, after even just a week or so of leakage you will see a build-up of mineral salts and corrosion at the flanges.

In our opinion a good time to fix this leak is at annual service at the end of the heating season, when it will be less inconvenient to shut down, cool off, and possibly drain the heating distribution piping.

At below left is a little leak at the bottom circulator pump mounting flange [Click to enlarge any image] where you can see rust stains that do not appear on the sister circulators shown in the picture.

At below right you can see things getting a bit uglier on a different circulator.

Circulator pump leak at mounting flange (C) Daniel Friedman Circulator pump leak at mounting flange (C) Daniel Friedman

Below my ruler points to severe corrosion at the copper-to-cast-iron circulator pump flange.

Corroded leaky circulator pump assembly (C) Daniel Friedman

Why do circulator pump leaks go un-repaired?

Circulator flange gasket replacement (C) Daniel FriedmanWell the little leak at the red circulator at above left may not even be dripping onto the floor. Those hot heating pipes may be evaporating the small quantity of boiler water that leaks and runs down the pipe.

So nobody cares, right?

If you allow a leak at a heating system circulator pump to continue for too long, the plumbing and pump parts may be so damaged that the repair is both more difficult and more costly.

In the photo (left) we show a leak that continued at the Taco™ circulator pump mounting flange for long enough that the plumbing parts are badly corroded.

Instead of a "bolt-on" repair, additional plumbing work, and thus additional repair costs will be involved.

While the leak above appears to be due to poor sealing at pipe threads connecting to the circulator flange, most leaks occur at the circulator flange gasket itself.

The replacement gasket shown above is not exactly expensive - probably less than a dollar. So why do circulator pump leaks weep for attention?

I suspect it's because we notice these leaks during the heating season. It's cold outside.

Nobody wants to go to the trouble to shut down the heat and maybe have to drain the system just to install this little gasket.

If you do need plumbing repairs when replacing a circulator pump or pump flange assembly, this is a great time to ask your plumber or heating service technician to also install a service valve right at the circulator pump - if one is not already there. Having these isolation valves in place makes circulator repairs a breeze - well a comparative breeze.

Our next two photos (below) show a service valve added at a circulator pump (below left) - with a leak needing repair, and a leaking circulator pump at the mounting flange ( below right).

Control valve at a circulator pump mounting flange (C) Daniel Friedman Leaking circulator pump (C) Daniel Friedman

A working shutoff valve on the heating distribution piping at the circulator pump can reduce the repair time, trouble, and cost the next time that circulator pump assembly repairs are needed.

Also, if flow balancing valves are not already installed on the system, a valve at the circulator pump can permit balancing of hot water flow among multiple heating zones when all of the zones are calling for heat at once.

Our photo (above left) shows a valve at the inlet to a circulator pump on a hot water heating system. As the valve is leaking, this control valve will speed the repair process.

Video Example of Rapid Circulator Pump Leak

Rapid leak at Bell & Gossett Circulator Pump in Minnesota (C) KK

Our photo above, taken by our field inspector K.K. sports a blue circle around a rapidly-leaking older style B&G circulator pump on a Northern Minnesota home. [Click to enlarge any image]

Click on the circulator pump image below to view K.K.'s video recording (1MB file, MP4 format) of what we consider a serious circulator pump leak.

Movie of leaky circulator pump (C)  KK

What should you do about a rapid circulator pump leak like the one in the photo and video above?

Our on-the-scene field consultant K.K. took the following steps:

  1. Determine that the boiler leak rate is significant - rapid dripping that fills a coffee can in a half hour is in our opinion a fast leak. A rapid heating boiler leak needs prompt repair by a trained heating service technician.

    We needed to decide if we could leave heat-on and we needed to decide if we needed to make an immediate emergency-heat-repair call (more expensive than normal service) or if we could wait until morning of the following day.
  2. Decide if it is safe and desirable to leave the heating system in operation.

    We discussed the state of repair of the heating system, confirming that the service company had just recently installed a new automatic water feed valve. An automatic water feed valve will feed make-up water into the system if the system pressure falls below 12 psi - a condition that occurs normally when the system is cold (that is, heat has been off for a time) or at any time if so much water leaks out of the boiler that its internal pressure drops below that setting.

    We decided that in this case it was safe to leave the boiler turned-on, a desirable choice considering that the home, located in Northern Minnesota, was facing high winds and low temperatures, risking both uncomfortable occupants and damage from freezing pipes if heat were turned off and if we could not obtain very quick repair service.

    Watch out: Most residential hydronic (hot water) heating boilers in North America don't have an automatic low-water-cutoff valve (LWCO) though that control can be added, and it's found on virtually all steam boilers.

    A heating boiler that is not shut off when it has lost its water supply is unsafe, risking a BLEVE EXPLOSION or permanent damage to the boiler. So if we thought that the boiler water level would not be maintained, or if we saw steam coming out of the boiler's temperature/pressure relief valve, we would have had to shut down the heating boiler immediately - by turning off its power switch.
  3. Avoid water damage to the building. While this boiler leak was in a garage with a concrete floor and a working floor drain, our on-site field inspector decided to place a bucket or container to catch leaking water - see photo and video above
  4. Call the heating service company for repair. A call to the local heating service company the following morning led to a prompt service call. The heating service technician agreed that the circulator pump was leaking - most-likely around the pump bearing, a leak that is not field-repairable. He replaced the circulator pump with a new one.

Circulator Pump Bearing and Circulator motor failures on hot water heating system pumps and what causes them: circulator pump mounting and support errors

Circulator pump mounting assembly (C) Daniel Friedman

On some circulator pump models, including older B&G circulator pumps, we have found leaks at the pump shaft seal that connects the electric circulator pump motor to the actual water pumping assembly.

Several causes for leaks at the circulator pump shaft bearing or pump seal

At a heating system inspection we found a pile of five or six circulator pump motors in the corner of the boiler room.

The "beginner" heating tech had replaced each circulator pump motor after less than a year of service, thinking that she was simply getting "bad parts" from the supplier.

The root cause of the bearing and circulator pump motor failure in this case was not "bad parts" - rather it was that the bracket holding the circulator pump motor was not properly mounted and was slightly askew.

This out-of alignment of the circulator pump motor mean that the motor shaft was "torqued" through its sleeve bearing, leading to early circulator pump bearing failures, leaks, and noises.

Our photo above shows the mounting assembly intended to support the electric motor that operates a hot water heating system circulator pump.

Hot Water (Hydronic) Heating Boiler Circulator Articles


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