Can't have dhw and ch at the same time

14 Apr 2009
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United Kingdom
I have a vokera Mynute 14se boiler contolled by a Danfoss Randall TP9 timer,because of a leak we had a motorised valve replaced (previous post) all works well untill i try to boost the hw if the ch is on , or boost the ch if the dhw is on . The red light comes on but there is no "click" at the contoller unit . I visited my neighbour who has the same heating and controller and tested her unit,the red light comes on and the controller clicks when i boosted the ch and then dhw . I've spoken to the engineer who replaced the motorised valve and he seems to think that a new controller is needed but i would like your opinions aswell.
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Sounds likely that it is the programmer. It's the same wiring that operates the heating and hot water regardless of whether it's on the +1 hour boost, or normal timed settings. If the timed settings are working as they should (ie allow you to have dhw & ch on together) then the wiring from the programmer onwards including the motorised valve will be OK.

I'm not too familar with a TP9, but on most programmers, there is a click from a relay when the boost is operated. Odd that both boost functions have failed at the same time though. Maybe they share common internal components.

If you are able to use a multimeter then you could test it, you will probably need to run some wires from the backplate to allow you to replace the front and operate it. Fix the wires to some terminals or a juction box that will allow you to connect the multimeter leads. Only carry out this test if you are competent though. Make a neutral connection to terminal "N" and a live connection to terminal "4" operate the heating boost setting and see if you get 230 VAC across the two points. To test the boost for the hot water use "N" and "3"

Thanks stem, my son is a 3rd year apprentice sparkie so i'll get him on the case.Have a good Christmas :D

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