Thermostat change

[emphasis303]

hi

My friend is having trouble changing his stat, he is not sure what the wires are, he has a blue, a brown and a yellow&green, the yg is lighting the bulb on the screwdriver tester and so is the blue, he has 2 terminals on the new stat, one says A one says B the third is COM but that is got a little plastic cover over it which can be broken off if the port is needed.

The wiring for this was done around 1986 and the wire is flex wire.

If he puts the blue in the port A and yg in port b what happens to the brown?? Also would that be the correct wiring method

If anyone has any ideas please post as ive never done anything with stats
thanks

p.s the instructions are available on the link

http://www.screwfix.com/prods/40819...t;jsessionid=CM4TB2KC0RVTMCSTHZOCFFI?ts=80578

 

[emphasis303]

any ideas guys?

 

[Spark123]

My thoughts are it sounds dangerous as he is getting power on a core which should only ever be used as a CPC.

 

[emphasis303]

thanks for the reply, yeh from what hes describing I hate to think what hes got himself into, but he has said hes going for a rewire this summer but for now he just wants to sort the stat.

Where would the wires go and what wires are what?

 

[Spark123]

You need to look at the other end of the wiring and see where they are connected at the boiler, personally I'd be tempted to try and get a 2 wire version so the brown to L, Blue (brown sleeve) to Ls and the green/yellow to the earth terminals.

 

[emphasis303]

but the earth wires has a current running through it? Does he still attach it to the backbox? and brown to A and blue to B

 

[daytona]

no,do not attach it to anything until you sort out the earthing problem.it could be a few volts or it could be more serious.you need to know why.throw the neon in the bin and get the multimeter on it.you need to sort this out before you even consider the stat.

cant you link the stat terminals at the boiler to get it working?

 

[Spark123]

The one he has bought is suitable for 2 wire operation, so there is absolutely no need to use the earth core for anything other than what it is designed for. It needs to be connected to the earth terminal at the boiler end and to the earth terminal at the thermostat end.

 

[emphasis303]

Hi

the boiler is working i dont know how but he says the boiler comes on and just heats the rads then switches it self off and on when it starts to go cold. Im going to go and see him tmrw or sunday but wana be prepared before i go so i know what to do and dont waste time.

I read on an earlier post that the earth could be being used as a switched live, he says that the wiring by his boiler is a mess and hes not sure whats going where as theres too many wires

 

[Spark123]

You must never use an earth core for anything other than earth.

 

[emphasis303]

lol yeh I know but try telling his dodgy electrician in the 80s that

 

[Spark123]

Your best bet is to trace the wires at the boiler end, find out where they connect and to just use the brown/blue cores for the permanent/switch live. Connect Permanent live to A and switch live to B. Connect the earth to earth at the boiler end.

 

[emphasis303]

Thanks for the reply,will try this and get back to u any other soloutions would be appreciated

cheers

 

[daytona]

as long as the stat cable isnt damaged half way down the run. earth not connected at stat end if not connected at the other end dont connect it to anything .dont want to blow up the boiler now do we?

 

[salem2000]

Tell your friend to throw the tester screwdriver in the bin and get a multimeter. These things are nothing but screwdrivers and nothing more, the voltage may be caused by induction, the only way to be sure is with the proper equipment. I'm sure they would show voltage present even when picking your teeth given the right conditions.