Grundfos Pump earth fault after bleeding air ? HOW ?

[Gnarly Neil]

I have had an airlock on my pump so I opened the air bleed screw in the middle of the pump after sorting out the airlock by draining off some water from a rad water was dripping slowly from the pump bleed screw hole. I tighted it up , Ran the system and felt very pleased with myself ...........

Then the RCD tripped and sickening feeling hit my stomach.... oops.

I can run everything fine with the pump disconnected from the wiring panel . The boiler fires up and heats the water . Without the pump running I only let it run for a bit as you can hear the water starting to think about boiling !!.

The resisitance was about 200K ohms between L or N and Earth. With getting the pump body hot all day it seems to have gone up to Inf so I connected it back up. It still blows the RCD out. I measured the other way and appear to have a rectified loop.

I can't understand how the water got to the "electrical" side of the pump. I have not stripped the pump down yet and am not sure if they are "servicable" to that level but I suspect some arcing during the "wet" fault that has left a track for the rectified leakage current.

How is the pump constructed.

No water has got to any of the external fixtures on the pump it ran down the outer casing from the blled hole?????

HELP

 

[simond]

It isn't necessarily the water that has caused the insulation breakdown. If you have been running the pump dry it will cause overheating and you could have compromised the insulation in this way.

I suggest you just change the pump, assuming it is an external domestic unit you are only looking at around £60-70 for the part.

 

[WDIK]

you have an in excess of 30Ma leakage current to earth via your pump.
how it happened?

it happened, was the terminal box at the top?

either way it wont recover, change it and get used to the idea.

 

[Gnarly Neil]

yes the ternimal box was at the top and there is no way that the water could have got in there.

I am not sure it was due to the pump running hot as the resistance was very low when it first failed. With a day of "drying" it had improved dramatically. Was initilally about 200K in alll directions now just a recified loop of about 400K which gradually climbs as you watch the meter. I know these motors have a capacitor in them, I could be seeign some effect of that with my meter if it is that that has gone to earth? may be.

Strange one .....

I am in the process of getting the whole system changed for a new condesing boiler and a new unvented tank.... That was going to be next week. It would have been good to get the pump going to he;lp with flushing before the change over.

 

[Agile]

The seal beween the water and the winding relies on the washer which the pump bleeding screw tightens into. You may have over tightened the screw!

They can sometimes be recovered by removing the head and putting them on a hot area to boil the water off or in an oven at about 150°C for an hour. Or judicious application of a hairdrier.

But you may still have a leak around the screw. If so then a bit of PTFE tape may seal the thread.

Or just buy a new pump, you know that makes sense!

Tony