central heating coming on when only hot water selected

[jpgibbo]

when only hot water selected my radiators get hot. I have checked wiring and it all seems wired correctly for a y plan system according to honey wells diagrams. I have proved the 3 way valve is not sticking by wiring a new one in as a dummy and watching it move between ports. The valve irks fine when ch selected and closes port to hot water, when both selected it stays in middle but when hot water selected it moves over to cover ch port but not all the way and does not seal.
The programming unit used in system is a siemens rwb-9 and the dip switch is set to 16 on the back to allow both to be called for independently but when i have checked with multi meter there is 240v on terminal 4 on programmer which is ch on?

Is it possible that the siemens unit is faulty. For hw only i should have 240v only on terminal 3.

 

[TCCHeating]

If the 'dummy valve' you wired in is behaving like the current valve is, then it must be an external fault. Are you getting stray voltage from anywhere, room stat maybe? If not suspect siemens programmer.

Try linking the programmer out and see how the valve moves.

 

[jpgibbo]

Thanks.

Every other part of the system is working fine, both wall stat and cylinder stat operating fine and cut boiler out and start it up as they should.

Siemens programmer Pin 1 = hw off
Pin 2 = ch off but is not used as stated in diagrams
Pin 3 = hw on
Pin 4 = ch on

With both ch and hw off i have 240v on pins 1 and 2 and 0v on 3 and 4 which is correct.
With only ch on i have 240v on pin 1, 0v on pin 2 and 240v on pins 3 and 4 which is wrong
And with just hw selected i have 0v on pin 1 and 240v on pins 2, 3 and 4 which is also wrong

 

[Hugh Jaleak]

Which valve do you have?

 

[jpgibbo]

honeywell 3 port mid position valve 22mm v4073a

 

[Hugh Jaleak]

Rules my theory out then....