Change Switchmaster 905 for Drayton SM2

[Team57]

I have replaced the above but found there are two extra wires 1 black 1 red in the old 905 that went to a terminal marked B on the back plate but did not connect to anything on the timer. I have taped these off in the new SM2. Most things are now working, clock, water is heating and boiler fires up. However the rads are not getting warm and the pump does not seem to be going. Could these extra wires have been for the pump?

 

[electronicsuk]

Even if it wasn't used as part of the programmer, if both wires went to the same terminal, then presumably they were linked? If that's the case, you should still link them together even with the new programmer. Just use a single 10A terminal block as a replacement for the extra connection on the old programmer.

 

[Team57]

Matthew

Thanks for reply, on the SM2 there is a 'link' it says for pumped systems remove it or gravity leave there. Whilst I have a pump, I am not sure if its a fully pumped system. I have tried both ways and it does not seem to make any difference. Are you saying put the two wires black and red into the same connector hole - sorry to be thick

 

[electronicsuk]

Matthew

Thanks for reply, on the SM2 there is a 'link' it says for pumped systems remove it or gravity leave there. Whilst I have a pump, I am not sure if its a fully pumped system. I have tried both ways and it does not seem to make any difference. Are you saying put the two wires black and red into the same connector hole - sorry to be thick

If the system is fully pumped you will have 2x 2-port valves or 1x 3-port valve. If the HW is gravity, the pipework to the cylinder coil will not be connected to the pump.

If black and red were previously connected together in one terminal of the SM-905, but this terminal was simply a link on the backplate and not actually used by the programmer, then you shouldn't have disconnected and isolated them when fitting the new programmer.

Unless there is a similar spare terminal on the SM2 backplate that does not connect to or perform any function related to the programmer, you will need to buy some terminal strip and use it to connect the red and black together.

 

[LoveRocket]

Erm, if these two wires were connected together but not to anything on the old timer, then they should be connected together but not to anything on the new one.

Or am I missing something?

 

[electronicsuk]

Erm, if these two wires were connected together but not to anything on the old timer, then they should be connected together but not to anything on the new one.

Or am I missing something?

Nope, it's just the OP who's 'missing something' hehe