What I have is a back boiler that runs my central heating via a pump. The domestic hot water is gravity fed.
At present I have to turn the domestic hot water on via a timer switch this then gives me hot water for the central heating pump to circulate when the room thermostat dictates.
I now have a Nest thermostat, this will sometimes switch the pump on earlier depending on the temperature outside so I connected both HW and CH to come on together via the Nest thermostat but because of it's properties the house may get warm before the hot water tank. If the HW is switched on manually then so is the CH pump.
Can I change the link wire with a wire with a diode and if so can someone spec it? The reason I want to do this is to keep it compact, the HW and CH will come on via the Nest thermostat but when HW switched only the HW will come on as the Diode should stop any power going back to the Nest and pump.
Room stat has been replaced with the Nest thermostat, N & L to respective position on Nest stat, 4 & 5 to 2 & 3 on the Nest.
for the heating to work the Nest starts the CH pump but only a timer stars the boiler(been like that since installation years ago) I have linked 1 & 4 together this means the Nest switches the pump on and the link starts the boiler = good enough! What this also means is that if the boiler terminal 1 is switched on then by virtue of the link the CH pump terminal 4 is switched on.
This is why I asked the question, to put a diode in the link between 1 & 4 so that switching 1 doesn't switch 4 on. I'm only suggesting this to keep within the existing footprint of these controls.
1 is switched live to boiler,2 is live (feeds 1 when switched on HW) 3 left vacant for this application, 4 is switched live for CH pump, 5 is live(feeds 4 when switched by room stat(Nest))