Replace an old Satchwell room stat with a Siemens RAA20-GB

Hi,
My old Satchwell room stat has thrown it's hand in. I have bought a new RAA20-GB from the plumbers merchants, but the wiring is completly different. I have a Baxi back boiler and old Glowworm Mastermind clock controller. The old Satchwell stat had red to terminals 1 and 3 and 2 blacks to terminal 4. The new Siemens has L live and Y1 and Y2, I have tried various combinations and it trips the circuit, I have put the earths together and insulated as there is none on the new stat. As far as I am aware, there is no motorised valve in my system, so I think it is only powering the pump and boiler, or not as the case may be.

Any help much appreciated.

warbuj said:

The new Siemens has L live and Y1 and Y2

Click to expand...

Do you have a multimeter?

If so measure the voltage between each red and the paired black. The red which measures 240Vac should connect to terminal L; the other red goes to Y1. The two blacks are neutrals, which are not required. Connect them to the same terminal of a terminal strip.

Thanks, the red that went to 3 was constant live, I have put this to L and the other to Y1. The 2 blacks are now in a block connector and the system is working. Managed to get this done last night as thought it might be another cold one.