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BillyS

Hello,
I hope someone can give some advice with this problem.
I have a Vaillant ecoTec plus 418 with Drayton MA1 mid-position actuator, Drayton HTS3 cylinder stat, Honeywell DT90E room stat and Drayton LP522 controller.
Boiler fires up reliably, but after it cuts out as soon as the DHW temperature is reached despite room stat being set above current room temp.
The reset (flame) button will not restart the system and the only way I can restart it is to switch off power to the boiler for a few seconds and then switch on again.
The Vaillant fault code is S.30 (no demand) despite the timer being on and the room stat being set above current temp.
The boiler runs reliably if I switch off DHW at the controller.
I have lived with this problem for a while and last year I replaced the thermostat and controller with no change to the problem.
I suspect the problem is in the Drayton mid-position actuator, but would appreciate some advice on how to check it out with a multimeter.
Many thanks for any help! Bill
 
Blocking / anti cycling probably does it come back on after 5-10 mins ?
 

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