Heating only comes on when hot water is selected

[CountryFan]

Really appreciate the time and effort in replies to this thread many thanks all. I have a much better knowledge of the issue now, I did contact one local plumber who advised the possible work around might be to use a wireless controller to get round the lack of hot water off lead.

What could be done, is move the programmer into the cylinder cupboard and alter any wiring needed if you want to utilise the 3 port, else stick in the 2 ports.

 

[Johntheo5]

I've allways found this Y plan and the MPV very ingenious but devilishly cunning when a fault occurs.

If the only problem is the missing HW OFF wire then is it correct to say that the CH will only work with both HW&CH selected and only while the cylinder stat is calling (to fire the boiler)??

Also, if the white & grey wire are joined together at /before the MPV will the system then operate like one with a diverter valve only, HW or CH.? On Ch only then the white wire will provide power to the grey wire to drive the valve fully over to the CH position only and the orange wire will then fire the boiler/. Presume it is a Y system and not a W system.

 

[stem]

Also, if the white & grey wire are joined together at /before the MPV will the system then operate like one with a diverter valve only, HW or CH.?

With Y-Plan, the motorised valve's grey wire should also be connected to the 'satisfied' terminal of the hot water cylinder thermostat (indicated by the red arrow below). Joining it to the white wire would then mean that when the hot water cylinder has heated up and the cylinder thermostat switches over to satisfied (i.e. goes off), when the grey wire becomes 'live' the white does too and the central heating would come on.

P.S. The room thermostat has been removed from the above diagram to fit the situation as described by the OP.

 

[Johntheo5]

Yeah, that's correct but if the the HW is off or programmed off, there is no voltage on the grey wire from either the stat satisfied terminal 2 or the HW OFF because its not connected but if the white and grey are connected and CH programmed on, the white wire which is permanently live will drive the valve to mid position, the second set of valve contacts will close and the first set open and because the grey wire is fed from the white wire then it should drive the valve fully over to the CH position, the orange wire should then fire the boiler?
My thinking is that if its used this way even temporarilly that HW or CH is available on demand, (separately), with both selected the CH will still come on (as pointed out) even if not required when the HW stat is satisfied and if it is required constantly then it will switch off each time the HW stat calls?

 

[stem]

Hmm. Sort of.. I think If I understand what you suggest, then:

When the CH was 'on' at the programmer and the white (CH on) and grey (HW off) wires being linked together are both made live, the valve will wind fully over to the CH only position.

Then, when in the above condition, and HW is required, the valve will still stay in the CH only position, and the HW won't heat up.

Once the CH goes off at the programmer, and the valve moves back to the HW only position, provided that the HW is still 'on' then the HW will heat up.

 

[ericmark]

If it did work, and now does not, some times latching the blead leaver on the three port valve will give a temporary fix, likely the micro switch inside the three port valve has stuck.

The DHW off wire, allows you to get CH without DHW, but it will work without it. But the DHW gets a bit too hot, not sure why you want heating in this weather?