Hi
Yesterday I had to replace a Grundfos circulating pump on a Combi Boiler.
The new pump was a direct replacement unit.
I switched off the 3 amp fused spur.
The cable/current/load for the 240v pump as far as I can see does NOT go through the boiler PCB (the computer board).
To connect the 3 wires to the pump I pushed the three soldered ends of the cable through a small hole (protective rubber piece),
as soon as all the wires touched the consumer unit TRIPPED.
I was always under the impression that that a fused spur has "a gap" when the switched is turned off.
But I checked the 3 amp fuse anyway, and this fuse HAD NOT blown.
So I pulled out the Slow Blow fuse that is positioned on the incoming side of the mains power. This slow blow fuse is positioned right
next to the PCB and I'm just guessing, but I would think this is to protect the PCB.
Holding the slow blow fuse up to the light that has a "clear glass" so you can see the fuse wire, the wire looks intact.
The slow blow fuse has "red stripes" going around the glass but one of the stripes is GRAY/BLACK - now I don't know if
the gray/black stripe has always been there or it is an indication that the fuse has blown.
Due to a serious problem with the connections block on the pump, the pump has got to be returned, so I wasn't able to
test the boiler to see if it was going to work.
The problem on the pump was down to the quick fit (no screws to connect wires), just push small orange plastic bit
with screwdriver to open each connector, to push soldered end of wire in, take pressure of screwdriver to close
the connector.
Unfortunately the middle block for 'live' was broken and I could not open the connector. I tried for hours to connect but had
to give up in the end, as the plastic bit was just floppy and there was no way to get at it to try and fix. The connector block
was fixed tight to the printed circuit board, that made it impossible.
So two questions;
If the spur fuse did not blow how/why did the consumer unit trip?
If the Slow Blow fuse has blown, would a slow blow fuse actually trip the consumer unit?
I will buy another slow blow fuse to be on the safe side, but do you know where I can get these type of fuses.
I haven't got the fuse with me but from memory I think the manual says it's 2 amp.
It is half the size of a normal 13 amp plug.
Any help or advise would be appreciated, as I really hope I haven't damaged the boiler.
Confused and now worried.
Many thanks.
Stephen