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.

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

Article Contents

• CIRCULATOR PUMP LEAKS
  • CIRCULATOR LEAKS at MOUNTING FLANGE - slow leaks, seepage
  • CIRCULATOR LEAKS at BEARING SHAFT - rapid leaks, urgent repair
  • CAUSES of CIRULATOR BEARING SHAFT or PUMP LEAKS

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.

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

Why do circulator pump leaks go un-repaired?

Well 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).

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

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.

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

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

• Age, wear, long-usage of the pump; these pumps often run perfectly for decades, but the additional troubles listed below can shorten pump life
• Failure to lubricate the pump shaft and bearings - something that should be performed at annual service.
• Worn, sagging circulator pump motor support causing torquing and wear of the bearings - elaborated below
• Overheating pump motor, possibly from a lubrication failure can cause bearing failure and leaks.
  
  A circulator pump itself can fail and can also damage the motor if mineral crud or corrosion in the pump assembly causes the impeller to jam. A bad starting capacitor can also cause pump motor failures but that probably doesn't cause pump leaks.
  
  Also see details at CAPACITORS for HARD STARTING MOTORS
• Possibly: leaks from above, dripping water into the pump motor or bearing shaft assembly from the outside. (Specluation on my part)
• Possibly: improper electrical wiring, routing wires around a pump or other hot heating system component can cause an electrical failure at the pump or elsewhere, risking a short circuit or failure - source: https://www.emergencyplumber.uk.com/plumbing/central-heating-pump-problems/

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.

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Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

On 2020-04-17 - by (mod) - faulty O-ring may explain leaky circulator pump - sources of Grundfos Röthenbach, Model 25-60/180 Circulators

Thanks for the added detail, René.

O-ring damage can be subtle yet cause leakage, especially nicks, dents, and of course the O-ring needs to be the right size. I've had good luck replacing them just as you tried

Years ago Dan Martin pointed out to me that many machine parts, including O-rings, are not going to be unique to the machine - the cost to the manufacturer would have been too great; so we can usually find an off-the-shelf replacement that will work.

Glad your air purge and leak are solved; your notes will help other readers; I'll be sure to keep your remarks with the article.

The Röthenbach, Model 25-60/180 looks very much like pumps sold world-wide under many brands like Grundfos, Lenntech, Ferro, etc, all of whom sell a circulating pump with the identical model number;

I suspect they're all the same design, licensed for sale under various brands in various countries including the NL (Netherlands, not "Newfoundland and Labrador", right?.)

Your pump, bought through Amazon, or a very similar model with the same model data is
supported in the Netherlands by
Netherlands
GRUNDFOS Netherlands Veluwezoom 35
1326 AE Almere
Postbus 22015
1302 CA ALMERE
Tel.: +31-88-478 6336
Telefax: +31-88-478 6332 E-mail: info_gnl@grundfos.com

also available from

Grundfos Poul Due Jensens Vej 7
DK - 8850 Bjerringbro, Denmark
Tel.: (+45) 87 50 14 00 | Fax: (+45) 87 50 14 02
CVR 31 85 83 56

- so if you need parts in the future I'd give them a call

Here is a similar Grundfos Circulator Model 25-60/180 product data booklet from Lenntech

From a typical (Australian) product description (for other readers)

The circulator pumps in cast iron pump housing version are specifically designed for heating systems. For underfloor heating systems, it is advisable to use the stainless steel version, type Aphla N and UPS N, as the pumped liquid may often become aerated, causing an ordinary cast iron pump housing to corrode.

The Grundfos UPS 25-60 (180) UPS Light Commercial Circulators UPS pumps constitute a complete range of 3-speed circulator pumps. The pumps can be used in both open and closed systems. UPS pumps are of the canned-rotor type, i.e. pump and motor form an integral unit without a shaft seal and with only two gaskets for sealing. The bearings are lubricated by the pumped liquid.

Glad your air purge and leak are solved; your notes will help other readers; I'll be sure to keep your remarks with the article.

On 2020-04-17 by René - Röthenbach, Model 25-60/180 O-ring replacement

Hallo (mod)
Thanks for your reply.

Brand is Röthenbach, Model 25-60/180 bought at Amazon. See the picture on my previous post. I live in the NL. I emptied the circuit this afternoon and removed the front screw. Behind the screw, there is indeed a slot to manually turn the pump motor/assembly.

Sorry that I cannot post a picture since I only read your mail after having reassembled and refilled the installation.

The o-ring appears to be slightly dammaged (see in front of the match), and I cannot swear I did not do it. I had the impression that the internal diametre of the o-ring was (far) broader than the screw diametre and that its "seating" on the pomp.

For these reasons, I replaced it by a -tighter- new o-ring from my garden watering installation (Gardena). Maybe, one day, I'll buy a better one. Anyway, the leakage did not occur any more. In order to avoid repeating the issue, I did not purge the installation. All bubble noises ceased after 1/2 hour running.
Thanks for your interest and support.
René

On 2020-04-15 - by (mod) - leak at access screw on end of Grundfos / Rohtenbach circulator pump

René

Can you tell me the brand and model of your circulator pump? Are you in the U.K. ?

Your circulator looks like a version of Grundfos, also sold under brands including Hyjet, FHS Pumps, JAAS Perry, Rothenbach, and other brands in he U.K. including, I think at least some versions made in China.

Do keep me posted. I'm looking for details from the pump company to see what they illustrate as a gasket for that screw. You could also put a small amount of teflon paste on the threads if they seem worn or nicked.

But don't blob the paste on as we don't want to push it into the pump.

Watch out: the circulators I've reviewed, seen, worked with, use a center screw to give access to a slot to manually turn the pump motor/assembly; on some models, with the screw removed, inside you'll see part of a printed circuit card:

I doubt that those models are intended to ever have water running through that part of the circulator pump assembly. So if you see water in such a location I'd worry that an internal pump seal has failed.

On 2020-04-15 by René

Thanks for your reply, mod. The fittings above are dry, that's why I suspect the screw or the gasket.

The pomp is feeding a solar collector

I'll purge the circuit as soon as the weather is less sunny, and check this %$#@# screw.
...And post a reply.

On 2020-04-15 - by (mod) -

René

If you've tried tightening the circulator vent screw and it still leaks, I suspect a damaged gasket or O-ring or, less likely, a cross-threaded damaged screw or screw mounting hole.

First let's make darn sure that the leak is really at that screw and not water leaking from the fittings above, sneakng around and appearing as a drop at the circulator pump bottom.

On 2020-04-15 by René

My (new) circulation pump leaks on the motor side. After installaion and filling, I purged air from it as indicated in the instructions by unscrewing the big screw on the motor side. Since that time, water (glycol) drops comes out at a rate of ~5 drops/minute from this screw, but only when in operation, at any speed.

What can be wrong? Damaged o-ring? Not purged enough?

On 2014-10-22 - by (mod) -

Matt

Unfortunately I suspect a leak at the pump bearing. If the leak continues when the system has cycled through both hot and cold intervals it's time to investigate further and possibly replace the pump assembly.

Check of course for a leak higher up at a replaceable pump mounting gasket.

On 2014-10-21 by Matt

great article. my circulator pump is leaking at a small weep hole located at the 6 o'clock position on the pump. I just started the system, and was wondering if this will stop? Is there a valve in the housing which could be replaced? Thanks very much.

On 2014-09-16 - by (mod) -

Anon

at

https://inspectapedia.com/water/Booster_Pumps.htm

you can see an illustration showing the effects of building height on water pressure or "head" as you put it.

On 2014-09-15 by Anonymous

Yes, "hot water heating system circulator pump". Plan to replace it with a B&G unit. Problem: Have a two-story home above basement, pump in basement. How much head is needed. Current 80 yr old pump is 1/6hp, single phase, 1725 rpm. B&G has myriad of pumps avaiiable but don't mention "head" in any description.

How do I know the motor/pump will handle my situation? One pump supple house is recommending B&G 102218 which is 1/4 hp, 16 head. That is: more hp than existing but have no way to compare head.
Thanks for the comment, JC.

On 2014-08-23 - by (mod) -

JC

If your water pump is leaking as you describe most likely an internal seal or bearing has worn out. It's time for a new pump.

I don't quite get why a water pump (meaning a well water pump) would be attached to a heating system - perhaps you meant a hot water heating system circulator pump.

On 2014-08-22 by j c lenahan

I have an approx 80 yr old Wagner Electric water pump attached to the home heating system of my 125 year old house. The pump is working fine. However, water is now emanating from the oil cap of the impeller. I have a picture of the leak site and the motor spec plate but do not know how to send it to you.

Question: is it possible to get impeller repair kits for one this old or would it be faster/simpler to pull out the entire motor/impeller unit and replace it? Scary part: pipes are very old as they were 37 years ago when I (personally) installed a new boiler.

Thanks for the great website. JC

On 2012-12-26 by Jacqueline W.

We have just paid approx $4500 for a new Bradford White wter heater to be installed. The water heater heats the water for our home, plus (in a divided tank, it heats the water for under floor heating.

From the moment it was installed the hot water for the house (sinks/showers/wash machine etc, worked fine. But the under floor heating was not working. period. We called out our Installer, who came the day after Christmas and told us the "pump" was broken and it would be another $850. Does this sound right?

On 2012-02-16 by Mike

I have a household circulation pump on my gas combi boiler. It started leaking profusely where the gasket is. Should I try a new gasket first or replace the whole pump?

...

Continue reading at CIRCULATOR PUMP MOTOR or BEARING Failure or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see CIRCULATOR PUMP LEAK FAQs - questions and answers posted originally on this page.

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