CH pump blowing fuse after working fine for ages

[aberant]

Hi all. So this morning I got up to discover CH/HW was inop, discovered the 2 amp fuse in the wiring centre had popped. Purchased 2 more and replaced one in the hope it was a random thing. Went out, came back this evening to find it again gone. Put the other spare 2 amp in, to find out what was causing it. HW alone fires up fine, excluding boiler / cyl stat / programmer. Turned HW off, turned CH on and pop goes the fuse immediately.

So, to me the fault is either in the roomstat or the pump (or wiring between). I'm presuming the pump unless something weird is going on with wiring/stat? Any ideas why the pump would suddenly start blowing the fuse? Its been running fine for 2 years.

Cheers!

 

[cross thread]

just change it,only thing to check is water leaking on to electrics

 

[seco services]

if you have a gravity hw pumped heating then yes poss the pump has failed which is quite common when they fail to blow the fuse if the windings have gone etc.


disconnect the pump then try if it fires the boiler you fit a new pump.

 

[aberant]

Thanks for the replies guys, pretty much what I thought really. However, having nipped to ASDA to stock up on 3amp fuses, I've discovered this. If I touch the switched live to the pump onto the screw head at the top of the terminal, the pump *seems* to run fine, certainly it makes a sound which sounds like a pump pumping......
If I put the wire into the terminal and screw it down, the fuses pops instantly upon turning on. Why would this be the case? The first thing that came to mind was perhaps a stray strand of wire bridging between neutral and live or some such, but I can't see anything like that. This is very odd...

 

[JohnD]

water leak?

 

[matt1e]

Thanks for the replies guys, pretty much what I thought really. However, having nipped to ASDA to stock up on 3amp fuses, I've discovered this. If I touch the switched live to the pump onto the screw head at the top of the terminal, the pump *seems* to run fine, certainly it makes a sound which sounds like a pump pumping......
If I put the wire into the terminal and screw it down, the fuses pops instantly upon turning on. Why would this be the case? The first thing that came to mind was perhaps a stray strand of wire bridging between neutral and live or some such, but I can't see anything like that. This is very odd...

sounds like the capacitor (funny I've just been on about these) has gone
kaput.(lost some of its capacitance)
the motor will fail to start and will draw too much current and blow the fuse (usually within a few seconds)
just holding the live to the terminal may be just enough of a bad/intermitent connection to create enough of a phase shift to start it

Thats my theory anyway
Matt

 

[aberant]

not aware of any leak but this can be checked when I lift the board.

matt1e - where is there a cap in the circuit? Also, your theory matched mine ref the limited current - I was thinking along the lines of maybe not all strands touching the head thereby limiting surface area cross section limiting current flow....or something.....

 

[matt1e]

not aware of any leak but this can be checked when I lift the board.

matt1e - where is there a cap in the circuit?

depends on the pump!
smaller domestic ones usually have them mounted in the terminal block housing, bigger/older ones have them mounted on the outside

matt

 

[aberant]

Sorry matt my question was a bit ambiguous - I was unaware that a cap was used in control of the pump - what is its purpose in this case? This is new info to me is what I'm getting at, and i'm intruiged

 

[matt1e]

Sorry matt my question was a bit ambiguous - I was unaware that a cap was used in control of the pump - what is its purpose in this case? This is new info to me is what I'm getting at, and i'm intruiged

Hi aberant
without getting too technical its purpose is to give the pump motor a "kick start"
have google of PSC motors
matt

 

[aberant]

cheers Matt, will have a goosey. Fitted a new pump today, when I finally got access to the old one I wired it in correctly (took pics, will upload - was horrific!). After rewiring it didn't pop the fuse but didn't seem to be shifting the water either and was getting very hot before the water had heated up, and emitted a rather odd smell. I decided it had given up, new one fitted and all is now well! My thanks for the help.

Gregg (aberant)