potterton netheat problem with water and rads to work to get

[spandex]

Hi (sorry about user name only thing the dam system would let me have!)
Any way I have recently changed the tank thermostat on my water tank and all seems well until the water temp is reached. the controller clicks the red light comes on and then the radiators start to go cold until the water temp drops and the boiler starts up to heat water then rads also warm up until once again temp is reached and it all cuts out.
If i just put heating on all rads hot, if i just have water on then i get hot water. The system is a potterton netheat profile, can anyone help me?

 

[seco services]

sounds like a boo boo on the wiring
is it a y plan or s plan ?

 

[spandex]

I don`t Know how would i find out?

 

[seco services]

have you two motorised valves or one ? and how did you wire the stat up ?

 

[spandex]

It was just the tank thermostat, it has a two pin connecter in the water temp control box. I bought a new one and connected it I think it can only fit one way.
I have a drayton ma1 3 way valve under tank don`t think i have another valve as the pump is also set under boiler.

 

[spandex]

I have not long moved to this house and one thing that i am not sure about is this, we don`t have a room thermostat only the water thermostat in the airing cupboard. I just wonder if now we have replaced the tank thermostat that it is doing its job and as we don`t have a room thermostat the heating has no way to know that it should still run to warm rads and so cuts out when water temp is reached?. That would mean that the syst has never worked properly i wonder if that was the case wouldn`t the last owners have done something to correct this? Its a mystery to me.