Fuse keeps blowing re: central heating system

[bluegambler]

Hi,
I have a 20 year old system - Potteron wall hung with 2 x 2 port motorised valves.
I noticed a faint burning smell yesterday from the airing cupbiard where the pump and motorised valves are - Also the electrical isolation switch is there.
And noticed later in the day that the lights on the programmer were not on, and there was nothing working.
I changed the fuse, and after sliding the controls over to ON the fuse blew.
I have tried having heating only and hot water only and always fuse blows.
I have even changed one of the synchron motors as thought the old one smelt a bit burnt.
I changed the other synchron motor last year.
I have undone the screw on the front of the pump and rotated the inner screw to ensure that it isn't stuck.
If anyone could offer any advice , I would be extremely grateful.

 

[gas4you]

First I would suspect the pump, even though it turns via the screw with a screwdriver. Second I would suspect one of the 2 port valves. Has any water leaked on either of these? As the smell of burning is in the airing cupboard I would certainly investigate here first.

 

[bluegambler]

I changed the pump about six years ago - Grundfos - so hope its not knackered.

 

[giblets]

Whip the terminal box cover off the pump and have a niff there - sounds like pump. Six years is quite a good innings for a pump that does both htg & hw.

 

[bluegambler]

Thanks for that.
Yes I have undone terminal cover of pump and its slightly wet inside and smell of burning.
I take it only course of action is to change pump.
Still I'd like to know how water got in, as no evidence of leakage from outside - seems to have come through from inside body of pump.
Thanks again.

 

[gas4you]

Pumps can last forever or go after about 12 months, depends on your system and the state of the water in it

 

[namsag]

Shortest time i have seen a pump last is 5 minutes. An it was a pain in the ass to change both times.