Boiler internal fuse keeps blowing together with the pump

[vinux]

I am confused , I wondered when you said you had tried a different pump this boiler should have a Myson CP 53 pump only, no other make should be used I have seen Ideal multi-heads being used but wouldnt recommend it but they will fit

Two different makes were used (Grundfos and Bosch) and only the pump head was replaced by the plumber. Is this the one I need then?

http://www.plumbclick.co.uk/circulating-pump-cp53.html

For this price I am happy to give it a try.

 

[JohnD]

are there signs of sediment and dirt in the water?

 

[vinux]

it is very difficult to make a pump fail unles it is dry. Even when jammed with sediment or having no flow, the water will help absorb the excess heat for several hours, but they will be noticably hot.

I really wonder what went wrong with yours.

I don't think it was dry, because the pressure seems to be above 1bar. I can't imagine that there would be so much dirt/debris in the water for it to have no flow.

I spoke to the plumber who replaced the pumps and he is just guessing now. He's got a theory that because a non original pump head was used the bit that actually pushes the water (propeller?) in the pump body started to touch the body wall and it got ceased eventually. Which resulted in overheating and shortening out. I saw that the axle on the pump head moves along the axis a couple of millimetres which I guess is normal for all pumps (no?).

 

[vinux]

are there signs of sediment and dirt in the water?

Some but the plumber assured me that it's nothing to worry about and he's seen much worse. The water is not brown.

 

[ianmcd]

I am confused , I wondered when you said you had tried a different pump this boiler should have a Myson CP 53 pump only, no other make should be used I have seen Ideal multi-heads being used but wouldnt recommend it but they will fit

Two different makes were used (Grundfos and Bosch) and only the pump head was replaced by the plumber. Is this the one I need then?

http://www.plumbclick.co.uk/circulating-pump-cp53.html

For this price I am happy to give it a try.

yep thats the correct one just split it and use the head

 

[dhutch]

yep thats the correct one just split it and use the head

Would it not be wise to try replacing the lot?

 

[JohnD]

yes, especially as there is a suspicion that the impellor has jammed?

does anything electrical ever go wrong with a pump except for the capacitor failing?

 

[ianmcd]

yep thats the correct one just split it and use the head

Would it not be wise to try replacing the lot?

It wont fit the pump bodies are completely different

 

[andytw]

I wouldn't think the fuse is making any difference. If you had them the other way around then it could be a problem i.e. It specifies a 'T' time delay fuse and you fit an 'F' fast blow fuse.

You say it fires up if you disconnect the pump. Where are you disconnecting the pump ? (At the pump or at the boiler ?)
When the pump is disconnected measure resistance (meter on ohms). between its L and E connections and between it's L and N connections, what readings do you get ?

andytw

I unplug the pump where the wire goes into it (L, N and E).

Measured the resistance, between L and E I get 1.
Between L and N I get 26.

So looking at these figures at face value you have 26 ohms between live and neutral which probably is about correct. The load is inductive so the actual resistance is only a guide.

However if you only have 1 ohm between live and earth then that is not good, it should be virtually open circuit of hundreds of megohms.

Are you saying you get a reading of 1 which is virtually the same reading as when you connect the meter probes together ?

Next step for me would be to get a length of mains cable and a plug and wire it to the pump. Make sure you connect all 3 wires L,N & E.
Make sure the plug only has a 3 amp fuse fitted. Plug it into the mains and turn on. Does the pump run or does it blow a fuse.
Take care, keep hands in pockets.

andytw

 

[vinux]

However if you only have 1 ohm between live and earth then that is not good, it should be virtually open circuit of hundreds of megohms.

Are you saying you get a reading of 1 which is virtually the same reading as when you connect the meter probes together ?

Next step for me would be to get a length of mains cable and a plug and wire it to the pump. Make sure you connect all 3 wires L,N & E.
Make sure the plug only has a 3 amp fuse fitted. Plug it into the mains and turn on. Does the pump run or does it blow a fuse.
Take care, keep hands in pockets.

andytw

Yes, I have double checked, it's 1ohm between L and E on the pump. I get about 0.4ohm when the meter probes connected together.

It looks like I don't have 3Amp fuse anywhere so will have to go and get one before I can try connecting it to the mains.

By the way, thank you very much for the help.

 

[andytw]

Then almost certainly a fuse will go bang. The only thing that says that the motor winding has not contacted the chassis of the pump is your interpretation of reading the resistance. I am not in doubt about what you say at all.
.4 ohms would be exactly correct being just the resistance of the test leads and the accurancy of the meter. 1 ohm is bad news. This would draw 220 amps or so from the mains.
I would almost be inclined to not test it, but a 3 amp fuse would go quickly so you should be OK. At least that is an absolute test.
We don't, as a rule, connect things to the mains that we know have a problem.

It does sound odd that you have a second, or is it third, faulty pump. You really can't do anything electrical to it to cause this to happen apart from shoving a couple of thousand volts up. What about location, can it get wet ?

andytw

 

[andytw]

Worth a read //www.diynot.com/forums/viewtopic.php?t=74279

Just found it at the bottom of the page below your thread.

andytw

 

[ianmcd]

you shouldnt get any measurable reading between L&E but it doesnt mean that it is the pump, you will have to remove the wires from the pump then measure the resistance at the terminals on the pump with nothing connected if you stll get 1 then it is the pump

 

[vinux]

It does sound odd that you have a second, or is it third, faulty pump. You really can't do anything electrical to it to cause this to happen apart from shoving a couple of thousand volts up. What about location, can it get wet ?

andytw

There are no leaks anywhere.

 

[vinux]

you shouldnt get any measurable reading between L&E but it doesnt mean that it is the pump, you will have to remove the wires from the pump then measure the resistance at the terminals on the pump with nothing connected if you stll get 1 then it is the pump

I have tested at the pump terminals with the wires disconnected. Just to be clear, I actually don't get a reading when I check L and E. It just shows 1 as if I haven't touched anything with the multimeter probes.