Three Port Plus Two Port

Perhaps you would like Mr Hailsham to test it for you?

And then come round and bake you a cake :LOL:
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So are you now saying that you are uncertain if the "dirty" signal on the white wire may cause problems with the second motor or that the second motor could cause R2 / D1 to burn out? If so I am not prepared to spend £100 plus just to try it.
No I'm not saying that!

The rectified AC supplied to the white wire at SW2, from the orange wire through R2 and D1, will be be so low that it will have no effect. There are two reasons for this: the value or R2 is very high (270k) and the current is trying to go through the diode D1 in the reverse direction, so it will be negligible. Don't forget that any device connected to the mains can cause the mains supply to become dirty, e.g spikes when fluorescent lights turn on, washing machine motors starting, etc.

Another website's description of the workings of the MPV say that R1 is a 13k ohm 2watt resistor and R2 is 270k ohm 1/4 watt resistor. The value of R1 is chosen so the rectified DC is just enough to stall the motor in mid position. The main purpose of R2 is to supply a small AC current (less than 1mA) to the motor to help demagnetize the motor when mid position is no longer required.

R2 also reduces the current, via SW1, R1, R2 and the orange wire, to the pump and boiler gas valve .This means the pump and gas valve will be controlled by the HW stat (HW only and both HW and CH) or by the HW stat, via SW2 (HW only)
An extension of a heating system requires the flow and return to be connected BEFORE a three port control valve (similar to a by pass). The extension needs therefore to be controlled by its own two port zone valve. Where should the CH demand signal be taken from?

At first site the white wire on the three port valve would be the obvious point, but does this go up to 120 volts when the HW comes on? and what would the effect of this be on the 2 port valve?


Chuck the three port idea and fit S plan. But with an additional 2 port in order to check the flow to the new rads when DHW only is selected.
(Gasguru mentioned this earlier. Good advice)

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