CH and HW will not come on at the same time

[matpaulin]

Danfoss fp715 controller - Gloworm economy plus boiler.

I am having a nightmare trying to figure out what is wrong with my system. If I want HW I can get it or If I want CH I can get it. But I can't get both at the same time. The controller appears as if it is trying to fire the boiler but it just clicks on and off. We also have a lot of noise in the morning when the CH comes on (I have to set the timings so that neither is on at the same time) I changed the 3 way valve a couple of years ago and I am tempted to do the same again - However I am not convinced that this will solve the problem. Any Ideas out there ???

 

[joesoap]

I had a similar problem with my Danfoss FP75 (about 8 yrs old). I suspected it was the controller and replaced it with a Danfoss FP715. This fixed it, and everything is working as it should.

 

[MANDATE]

The controller should produce a voltage at the input to the room stat when CH is switched on. It should also produce a voltage at the input to the cylinder stat when the HW is switched on and when the HW is off there should be a voltage which can be checked either on the grey wire of the motorised valve or at the cylinder stat on one of the output terminals.

The start position for the motorised valve relates to HW only and the final position for the motorised valve relates to CH only.
The mid positon relates both HW and CH. The motor is driven forward from the start position against the return spring and when it reaches the mid position, the 230 voltage is replaced via another path using a diode/resitor circuit producing a lower DC voltage. This is sufficient to hold the motor against the return spring until either HW or CH is satisfied.
Either the room stat or the cylinder stat will be switched and either the arresting voltage will be removed and the motor allowed to return to the start position or it will be replaced with full AC voltage and then drive the motor on to the final position where it will remain until HW is again required.
If you can't get both HW and CH at the same time it suggests to me that the motor is not being arrested at the mid position.
This I think could be due to a faulty micro switch or the diode/resistor circuit in the actuator head.
If you can remove the actuator head you can observe it going to the different positions as you activate the cylinder stat and room stat so you will easily verify if it stops midway or not. Mind you it will be a bit slow, it seems to do nothing for a minute.
Even if the problem is elsewhere it well worth a few minutes to check the valve out.