Heating comes on when Hot Water only selected

[ollysez]

I've got a 3 way Drayton mid position actuator on my central heating system and I have noticed that when I select hot water only on my control panel the heating comes on as well.

After reading previous blogs I checked the valve is not stuck by turning off the power to the system. When I did this the lever on the side returned to the W position, far left. I pushed the manual lever on the end of the box to the right, it resisted but I could still move it and when released it returned to the left side position. I take this to mean that the valve is not stuck.

I turned it back on and switched the heating on only and the valve moved to the H position on the far right. I take it from this that the motor is working. I then switched the hot water on only and the lever moved to the M position and the box made a clicking sound.

Any suggestions why the valve would move to the mid positon when the hot water is selected?

 

[doitall]

Either the actuator is duff (sticking micro switch), or either the room stat/cylinder stat, programmer is duff.

Easy to check with a multimeter.

 

[ollysez]

Thanks for your response

I thought it must be something electronic, looks like I'll just have to buy a new actuator.