Help Required ... 3 Way Valve not always switching to Hot Water

Yes, I always assume because we only have the HW on once a day for an hour the tank stat will allow it to start 23 hours later.

What I’ve never checked is whether ours ever gets up to the temp set by the stat … 65 I think
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Sorry for the delay … B to tank coil and A to return (?)

Thats the way I might expect it, you say it makes a buzzing sound when trying to change to HW, but I would expect it to be de energized on HW demand but not sure with these diverter valves.
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Yes the buzzing is a bit random and not sure what the circumstances need to be, it could start at 7pm when it changes from HW to CH but it might 8am when we notice it … we just flick the fused spur off and back on again to solve it.
Domestic hot water (DHW) does not power the valve when required. It powers the valve when NOT required.

So central Heating (CH) off the valve should be at rest. Power to boiler direct from the tank thermostat vir heat link.

CH on, with heat link and DHW calling for heat. The valve moves to centre, and boiler still powered heat link and tank thermostat.

If DHW stops calling for heat, then the valve in motored all the way, and now boiler supplied vir valve.

If CH is then satisfied, the valve is held all the way across until DHW is called for, at which point valve returns to rest.

So fault unlikely to be valve.
Thank you Eric, you wrote ... DHW powers the valve when NOT required ... if I understand correctly it may account for the occasional buzzing ... it maybe only buzzes on the occasion of the hot water getting up to the tank stat setting during the 6am to 7am time slot - which on most days it presumably doesn't.

I'll re-schedule the DHW for 4pm tomorrow so I can be stood at the side of boiler at the point it should kick in.
Revisiting this again, looking at the model number, I think you do have a MPV (mid position valve) even though the descriptor on the valve actuator is a bit confusing, but it does say "3 Position Diverter Valve" if you just put both to boost now with both roomstat and cylinderstat turned up, see if both CH & HW start heating together.


Here is a very good schematic of the MPV and wiring, showing the valve in the HW position (spring returned), but with both HW & CH programmed off but with the roomstat calling.

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Thank you for your help John, I’ll study that and report back later with this mornings results.
Yes, as is vertically upwards but I know of a Grundfos selectric running upright for the past 18 years!., no, past 20 years, PC:0414

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I hadn't realised the pump needed to be in a particular orientation ... how should it be, and why?
Should be hozirontally, the pump thrust bearings arn't designed to take the weight of the pump rotor.

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