Electrical wiring help

I have a faulty switch for my hot water cylinder. I have changed switches here in the past and in the UK. When I install the new one it blows the main fuse so there is a problem. I have 2 blue and 2 black wires. Any suggestions, could it be a faulty switch?

 If it still trips when you have fitted a new switch, it sounds like a problem with the boiler. Try an extension lead in another socket and plug the boiler into it, if it trips then its defo a problem with the boiler.

Hi, boiler is only 2 months old. Strange thing is switch works when on but trips when it is switched off

 Are you sure you have wired it correctly, as it sounds like a dead short when in the off position.

Hi, sorry but what is a dead short. My knowledge is only DIY. I have put the 2 black wires into one side and 2 blue into the other

 Oh, have you tried what I previously suggested, plugging into an extension lead in another socket.

Hi, yes, everything works with that. Strange thing is with the old boiler when we put a timer switch onto it it quite ofter blew the breaker, that is why we bought a new boiler. The switch started to stick yesterday so that could have been the problem all along

 Try it without the timer, boilers when the initially come on can draw a huge current thus tripping the trip switch, also is it a cheap chinese timer switch???

I no longer use the timer as it is an eco boiler and yes it is a chinese switch so a trip to bricolage for me i think!!

 It sounds like your problem then, especially as you say it started to "stick", its probably starting to burn out. Get a decent switch and it should sort it.

Thanks, it's the new one that's chinese. The old one is the original, probably 10 years old now. Many thanks off to buy a real one