Grundflos pump seized, got a new one fitted, it broke 2 hours later. HELP

lkay90 · January 2019

We have a 10 year old boiler system. Our grundfos pump was slowly on the way out, scolding hot, not supplying heating to the radiators downstairs and kept seizing. We were able to unscrew the bleed valve and manually rotate the spindle with a screw driver, this solved the issue for all of 1 week.
Now the boiler ignites, heating goes upstairs then boiler cuts out after 1 minute not supplying heat to downstairs.
We had a new pump fitted yesterday, this worked for 2 hours then same thing happened, pump went scalding hot, doesn't vibrate or spin and no heating to downstairs radiators.
Please help! all heating engineers seem to be puzzled with the problem

hot_rod · January 2019

It could be the system has an air lock, maybe frozen? This would prevent flow and the pump would over-heat and fail. They are very durable, usually cooling them down is enough to get them going again. Purge valves would assure you have air bubble free flow in the system.

SuperJ · January 2019

How's your water quality?

lkay90 · January 2019

How would i know? We've bled radiators all clear water. Pump had some gunk in it but cleaned it out and then seemed fine. Also new pump was only in a few hours

lkay90 · January 2019

When we bled the pump there was no noise that came out. We did have air hissing out our main bathroom radiator twice this week when we bled it though?

SuperJ · January 2019

I suspect there must be an issue external to the pump.
How tall is the house/building, and what is the system pressure set to? Is the expansion tank on the suction side of the pump? Has your expansion tank bladder been setup properly, assuming you have one? Improperly setup expansion tanks make cause the system to relieve pressure/water when hot, and then suck in air as the cool. What does the system pressure do throughout a heating cycle as the system warms up and cools off?

What sort of dirt/air/mag separation do you have installed?

I recommend a proper micro-bubble separator between the boiler and outlet and the system pump(s) (assuming pumping away from the boiler).

On an older system or a system with a history of problems a dirt/mag separator on the return would be advisable.

Do you have some pictures of the system showing the boiler and system piping including the pump.

Pay special attention to any check valves in the system (including the one that might be hidden in the pump outlet), you can cause some really bizarre unintended things with extra/improperly installed/placed check valves. Did your new pump get installed with the check valve? Is it actually necessary?

Gordy · January 2019

Is it possibly an electrical issue? As @hot rod_7 noted those circulators are very durable. To go out in a couple hours seems unreasonable.

What model circulator? Is it an ecm variety? They don’t care for oxide debris in the system. So if it is an ecm, and the piping is iron then you should have a good system flush with a dirtmag installed.

I suspect if you are bleeding rads that system pressure is maintained at 12-15psi?

Steve Thompson (Taco) · January 2019

First it would be a good idea to confirm is the new circs shaft is spinning (remove the air vent screw and see if it's spinning like you did with the old pump).

If spinning I would recommend checking any Y strainers (remove the screen and clean/replace. Was it installed with an integral check valve installed (might be sticking)?

Over the last 10 years has there been any water treatment done or has anything that might have caused a lot of fresh make up water being added to the system?

This may sound stupid but also check of the new circ was installed so it is pumping the same way as the old one.

Ironman · January 2019

Any of the above could have caused your circulator to fail, but it's extremely doubtful the problem was with the circ itself.

You need to find what's wrong in the SYSTEM that's causing it.

I see this regularly where a customer calls me after they've replaced a couple of circs and they go bad in a matter of days or hours because they didn't know to look for the cause of the failure and how to correct it.

It's not unusual for a wet rotor circ to last over 20 years if the water quality is good. I've got a Grundfos that's 25 years old running 24/7 all winter on my outdoor wood boiler.

EBEBRATT-Ed · January 2019

I would suspect water quality or dirt, iron oxide. But I doubt that would cause a new pump to fail in that short of time

hot_rod · January 2019

Scalding got sometimes indicates a pump that got air-locked, boiled dry and seized up.

If it has an isolation valve downstream you should be able to choke it down and hear flow going thru.

sunlight33 · January 2019

Could it be a power quality issue that causes the pump to run hot then fail?

tim smith · February 2019

Did they replace the entire pump, ie velout and motor impeller assembly as one or did they leave the velout, the section tied to the pipes and just remove 4 Allen screws on round part of motor Assembly and replace that section! If the latter, we have been seeing the flow checks at 8-10 yrs wearing a groove in shaft of check and hanging closed. Take a picture (side view) of pump and we may be able to tell from color of body vs motor.

hot_rod · February 2019

tim smith said:
Did they replace the entire pump, ie velout and motor impeller assembly as one or did they leave the velout, the section tied to the pipes and just remove 4 Allen screws on round part of motor Assembly and replace that section! If the latter, we have been seeing the flow checks at 8-10 yrs wearing a groove in shaft of check and hanging closed. Take a picture (side view) of pump and we may be able to tell from color of body vs motor.

The plastic IFC Neoperl checks, Tim?

HotanCool · March 2019

Improperly operating PRV(water feed valve). A properly operating Pressure Guage tells all.

Grundflos pump seized, got a new one fitted, it broke 2 hours later. HELP

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