Temporarily need hot water with thermostat (can't remember)!

[jackecole]

hang on i am going crazy now thinking about this wiring!! ha!

hw ony - orange live (as cy stat call is in same terminal box)

hw and htg - white and orange live

htg only - white, grey and orange all live

htg last off, grey has 230 v as valve held in last position.

correct?

 

[jackecole]

BTW when the valve is in mid position, the boiler and pump and turned on/off by the orange wire (which is operated by the motor from the 3 port moving across after power is applied to the white wire) if Honeywell

Wrong! The orange wire does not come into operation until the valve is in the CH only position. It just appears to be be providing 240v because it is connected to the same terminal as the HW stat CALL terminal.

if CH was only on then the cyl call switch would not be live - thus heating is put on by white wire making orange live (pump and boiler too) ??

 

[D_Hailsham]

hw only - orange live (as cy stat call is in same terminal box)

Correct. If you disconnected the orange wire from the terminal it would read 0 volts

hw and htg - white and orange live

The white is live from the room thermostat. The orange is live from the HW call, as above.

htg only - white, grey and orange all live

Correct. This time the orange is getting 230v through the valve and the lead from the HW call is dead.

htg last off, grey has 230 v as valve held in last position.

NO; it's the other way round. The valve is held at last position if the grey has 230v. This will only occur if either the HW is OFF at the timer or the HW stat is satisfied.

In this situation, the orange wire will only have about 150v. The voltage is reduced to this level to ensure it is to low to make the pump or gas valve work. It's a "quirk" of the mid-position valve.

If the grey does not have 230V when CH is last off, the valve will spring back (literally) to the HW only position and the valve will be un-powered.

 

[jackecole]

I didn't end up "bridging" the gap as seco advised!... not that i don't trust you i just had a shower at my neighbours instead! Wired a new stat up this afternoon though and all is good now.

Anyway, have been thinking about your "bridging" trick and what I was thinking, was you said remove the 2 other stat wires from the terminal blocks, ie the cylinder stat COMMON and SATISFIED terminals. But removing the COMMON wouldn't allow the stat to work at all would it?

Sorry, am bored, but it would be useful to know in case of a future prob.