Vaillant VR66 wiring control centre causing heating modulation woes?

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That sounds good. In my situation, I would have the VR66 near the valves.

Mine is an open vent boiler.
Do I take it that the switch wiring in the motorised valves stays as it is then, whereby if either is powered up and is then open, there is a 230 V input to the boiler?
I see how if the VR66 has set the motorised valve open, it (VR66) would know what flow temperature it required from the boiler.
Also, if the value failed to open, I guess the boiler wouldn't fire at all.
Does that sound right?

Thanks for all the tips everyone.

The VR66 does not have any feedback from the valves, it never knows if they are open/closed, it only assumes that they are open when powered.
This is in part why a ABV is a requirement as the pump may start before the valve opens and stays running after its closed.
If the valve fails closed then what should happen is that the boiler gets stuck overheating then running on bypass etc.
If you are using it with a regular programmer then the boiler trigger is always live as long as there is a "demand", the boiler does the rest with VR66.
 
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The VR66 does not have any feedback from the valves, it never knows if they are open/closed, it only assumes that they are open when powered.
This is in part why a ABV is a requirement as the pump may start before the valve opens and stays running after its closed.
If the valve fails closed then what should happen is that the boiler gets stuck overheating then running on bypass etc.
If you are using it with a regular programmer then the boiler trigger is always live as long as there is a "demand", the boiler does the rest with VR66.

Does that also apply to the VR65 combined with a VRC 470f?

If I nudge the temperature up on the 470, there is a noticeably long pause, whilst my 3-port turns to the correct position, before the pump runs and the boiler does its initial purger before firing.
 
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Using a VRC is slightly different as you do not toggle the boiler trigger as its always bridged and eBus just tells it to not fire.
Im sure there is some hysteresis on the VRC controller so it takes a few seconds before it applies your change.

The VR66/65 does not know anything about if you are using a 2/3 port valve. The delay will be the same on either setup.
As it does not know anything about the position of the valve it just adds a default delay which assumes the worst case scenario, my CH valve is slower than my HW valve.
 

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