Drayton Mid Position Valve fault

[Brooksiexxxx]

Just wanted to tell you guys about a fault that occurred on my CH /HW System using the Drayton 3 port mid position valve.
The problem was that my CH system would come on, but would continue to run at full tilt ignoring the room stat, or switching the CH off from the programmer. The only way I could stop the whole house getting very hot was to kill the mains to the whole system. H/W worked fine, with the tank stat controlling the temperature.
After some head scratching I disconnected the room stat output, and measured the CH Call voltage. When the fault occurred there was around 95V AC on the boiler input/call terminal.
The question was where was this coming from? I replaced the boiler control PCB just to ensure there was not a problem on the PCB outputting AC on the terminal, this made no difference. I checked the wiring in the junction box and everything looked ok. Looking at the circuit for the mid position valve I concluded that maybe one of the switches in the actuator was faulty, and the voltage was coming from there. Further inspection inside the actuator I spotted the black plastic arm that clips onto the valve/motor actuator arm had split, so although the valve moved, the switch was not being actuated by the cam on the end of the arm, hence stayed closed and put 230v through the call circuit continually. Replacement of the whole actuator has solved the problem. Had me scratching my head for some time though...

 

[rules&rulers]

After checking the system is wired correctly (so many are not,just see how many people come here and ask why their newly diy fitted rf/wifi thermostats dont work) ) Then its a logical approach with a multi meter to determine the fault,basic checks that just take 10 minutes if that.

Any you sorted it out and have spare pcb for when that goes wrong.

edit,your not allowed to change the pcb,others will explain.

 

[Agile]

The orange wire on a three port valve can be connected to the mains 230v via a 280k resistor. Probably why you were measuring the 95v.

Depending on the input impedance of the boiler call for heat terminal, that can sometimes cause false triggering the boiler. Some Worcester boilers were particularly troublesome in this respect. A quick fix was to connect a capacitor between the call for heat and neutral. I think all the latest boilers have been modified internally to prevent this problem.

Tony

 

[AGAS]

The question was where was this coming from? I replaced the boiler control PCB just to ensure there was not a problem on the PCB outputting AC on the terminal, this made no difference.

probably been cheaper to get someone services and a 20 min job . but hey your pleased with yourself now

 

[Brooksiexxxx]

Yes, I am chuffed that the fault has been traced and fixed, I had looked on forums to see if anyone had come across this fault before, is this a known defect with the Drayton actuators?
I was concerned that if I got your average plumber in to find this, they would struggle with such an odd fault..could have been v expensive for me
As I installed the system some years ago I was fairly confident that I could sort the problem out myself, and was hoping to find an answer on a forum rather than tracing it the hard way...
I had to change the whole valve as the old actuator does not come off the valve, and didn't want to drain the system etc if I could avoid it..anyway, job done and I've now got a happy family cos the heating works correctly again!! (maybe needed in the fantastic British summer weather!!)

 

[AGAS]

I had to change the whole valve as the old actuator does not come off the valve,

why was that ?

 

[Brooksiexxxx]

On the older valves the actuator is screwed to the valve, on the new valves the actuator has a release button allowing the actuator to be removed from the valve body. The two are not interchangeable, even the internals are slightly different so I had to change the whole valve...