Honeywell T40 Wiring

[D_Hailsham]

Wouldn't these be better the other way around?

Yes. Swap the wires connected to terminals 1 and 3.

 

[Ackoman]

Yes. Swap the wires connected to terminals 1 and 3.

Hang on, I'm confused now - do you mean swap the wires on the thermostat and do nothing with the other end?

I had concluded that the thermostat is wired correctly but that the colours are not ideal in that they have chosen yellow for the live and red for the switched live - am I mistaken?

 

[AGAS]

 

[D_Hailsham]

Hang on, I'm confused now - do you mean swap the wires on the thermostat and do nothing with the other end?

I had concluded that the thermostat is wired correctly but that the colours are not ideal in that they have chosen yellow for the live and red for the switched live - am I mistaken?

I'm also confused, so I have reread your posts; and you may be right. Here's a way to check

1. Forget wire colours
2. Is Terminal 1 live when CH is ON at programmer - irrespective of thermostat setting?
3. Is terminal 3 zero volts when thermostat turned down and CH is ON at programmer
4. Is terminal 3 240v when thermostat turned up and CH is ON at programmer

If the answer to all three questions is 'yes', the thermostat is wired correctly. If terminal 3 gives the results expected for terminal 1 and vice versa, the thermostat is wired incorrectly; swap wires to terminals 1 and 3 at the thermostat only.

PS If you measure between the terminal stated and terminal 2 you will also confirm that terminal 2 is connected to neutral. (No voltage on meter for all three tests = terminal 2 not connected to neutral.)

 

[Ackoman]

I'm also confused, so I have reread your posts; and you may be right. Here's a way to check

1. Forget wire colours
2. Is Terminal 1 live when CH is ON at programmer - irrespective of thermostat setting?
3. Is terminal 3 zero volts when thermostat turned down and CH is ON at programmer
4. Is terminal 3 240v when thermostat turned up and CH is ON at programmer

If the answer to all three questions is 'yes', the thermostat is wired correctly. If terminal 3 gives the results expected for terminal 1 and vice versa, the thermostat is wired incorrectly; swap wires to terminals 1 and 3 at the thermostat only.

PS If you measure between the terminal stated and terminal 2 you will also confirm that terminal 2 is connected to neutral. (No voltage on meter for all three tests = terminal 2 not connected to neutral.)

The answer to all those is indeed 'yes', so I guess it's wired up correctly just with an odd choice of colours

 

[D_Hailsham]

The answer to all those is indeed 'yes', so I guess it's wired up correctly just with an odd choice of colours

The End!

 

[hertsboilers]

It's hidden behind the part showing the terminal numbers. The anticipator is nothing more than a small resistor connected between the switched live (terminal 3) and neutral (terminal 2). When the thermostat is calling for heat, current flows through the anticipator. This results in a small amount of heat being generated by the resistor, which warms up the bimetallic switch in the thermostat. This causes the thermostat to turn off earlier than it would otherwise do and reduces the hysteresis of the thermostat. When the thermostat turns off, the anticipator cools down. If the wires to terminals 1 and 3 are reversed, the anticipator is permanently heated, so it has no effect.

I know there is an anticipator in most of mechanical room stats, but didn't know the theory behind. Thanks!