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Central heating pump tripping rcd any ideas?


DanMax&Belle

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Hi,

Fitting a mains central heating circulation pump on 16amp Shorepower. Every time I’ve connected the pump to power it has tripped the rcd at the bollard - immediately. I was just testing it to see if it would run before sealing and testing the plumping for leaks. I took the unit back to Screwfix and replaced it with a different model. Brought it back and exactly the same thing happened. I can rule out the cable/socket/pump electric connection as I’ve plugged it in without connecting to the pump and no problems. I’ve also changed bollards to my neighbours and the same thing happened. Is the fact I’m trying to operate it dry an issue (surely they’re capable of a few seconds use running dry)? Perhaps central heating circulation pumps don’t work well on 16 amp shorepower? 

Thanks all.

 

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You have the wiring wrong somewhere. Neutral to earth short? Sure they can run dry for a while. Mains is mains wherever it comes from.

Bear in mind that the earth on the pump connects to your pipework which if copper is connected to your hull which if you have an inverter aboard is connected to the neutral on the boat, see what I mean?

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Is it an RCD at the bollard or one of the horrible combined ones (RCCBO I think) that trip on over current?
It is years since I worked in electrical/heating game, but sometimes pumps would be stuck; even new ones. This could cause an over current situation. Sometimes  a tap with a screwdriver handle freed them.

Edited by Guest
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25 minutes ago, Boater Sam said:

Bear in mind that the earth on the pump connects to your pipework which if copper is connected to your hull which if you have an inverter aboard is connected to the neutral on the boat, see what I mean?

If there were a permanent E-N link then the boat would be incorrectly wired and nothing would work on shore power without tripping the RCD. 

1 hour ago, DanMax&Belle said:

I can rule out the cable/socket/pump electric connection as I’ve plugged it in without connecting to the pump and no problems.

Do you definitely have L-N-E correct when it’s connected to the pump?

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If the pump is wired with 3 core mains cable, try disconnecting the earth wire and isolate the pump from the boat's metalwork (put on a piece of cardboard)   They do run ok dry for a few moments, but check it is not seized from non-use, although the stall current is  unlikely to trip a RCD.   The bleed bung can be removed and a screwdriver slot on the end of the shaft should allow a screwdriver to check the rotor is free to spin...

 

Nick

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10 minutes ago, Nickhlx said:

The bleed bung can be removed and a screwdriver slot on the end of the shaft should allow a screwdriver to check the rotor is free to spin...

Check this,

If the motor is stuck it will draw a lot of current. One house I lived in we used to have to free the pump at the begining of winter otherwise the power went off (mcb tripped) when we first switched the heating on.

Edited by Loddon
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9 minutes ago, Nickhlx said:

If the pump is wired with 3 core mains cable, try disconnecting the earth wire and isolate the pump from the boat's metalwork (put on a piece of cardboard)   They do run ok dry for a few moments, but check it is not seized from non-use, although the stall current is  unlikely to trip a RCD.   The bleed bung can be removed and a screwdriver slot on the end of the shaft should allow a screwdriver to check the rotor is free to spin...

 

Nick

He’s tried two. He’d be a bit unlucky if two brand new pumps were both seized I’d have thought. 

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Thanks for all your suggestions everyone. Believe it or not it was the flex that was the issue (one common denominator and all that) for some reason it was fine plugged in without a load but when connected tripped everything. Checked wiring a couple of times so wasn’t that. When I changed the flex it all worked. 

Cheers again. 

 

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