Honeywell T40 Wiring

[pgleesonuk]

I am looking to replace an old Honeywell T40, but I am a little concerned how it is wired currently.

I believe terminals 3 and 1 are connected the wrong way around.
Assuming red is live and yellow/green is switched live.

Untitled

• pgleesonuk
• 26 Mar 2013
• 1

Any opinions?

How could I test it?

Thanks[/img]

 

[seco services]

1 - Live
2 - Neutral
3 - SW Live

Turn your programmer on heating, wall stat at 0, terminal 1 should be 230v terminal 3 should be 0v

 

[pgleesonuk]

Thanks.

The connections were wrong.

 

[Ackoman]

I am looking to replace an old Honeywell T40, but I am a little concerned how it is wired currently.

I believe terminals 3 and 1 are connected the wrong way around.
Assuming red is live and yellow/green is switched live.

Untitled

• pgleesonuk
• 26 Mar 2013
• 1

Any opinions?

How could I test it?

Thanks[/img]

Sorry to resurrect old thread - mine is wired exactly the same way as yours - seems to be a common error, but still seems to work. Any ideas why they are being done this way?

 

[Dan Robinson]

If the anticipator is not being used it makes no difference.

 

[D_Hailsham]

If the anticipator is not being used it makes no difference.

Agreed; but the pic in post #1 shows the anticipator connected, so the live and switched live need to be connected the right way round (1 and 3 respectively) for the anticipator to work correctly.

 

[Steelmasons]

Agreed; but the pic in post #1 shows the anticipator connected, so the live and switched live need to be connected the right way round (1 and 3 respectively) for the anticipator to work correctly.

That will all depend on whether the brown core is call for heat from programmer or switched live...

 

[D_Hailsham]

That will all depend on whether the brown core is call for heat from programmer or switched live...

What I mean is that the wire from programmer 'CH ON' must go to terminal 1 (aka 'live') of the thermostat; the wire from terminal 3 (aka 'switched live') must connect to the boiler's 'on' terminal. Wire colours are irrelevant.

 

[Ackoman]

Agreed; but the pic in post #1 shows the anticipator connected, so the live and switched live need to be connected the right way round (1 and 3 respectively) for the anticipator to work correctly.

Forgive my ignorance, but where is the anticipator in the picture?

 

[D_Hailsham]

Forgive my ignorance, but where is the anticipator in the picture?

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.

 

[Steelmasons]

the wire from terminal 3 (aka 'switched live') must connect to the boiler's 'on' terminal. Wire colours are irrelevant.

Terminal 3 usually sends voltage to motor valve or if gravity hot water then term 3 powers pump.

 

[Ackoman]

1 - Live
2 - Neutral
3 - SW Live

Turn your programmer on heating, wall stat at 0, terminal 1 should be 230v terminal 3 should be 0v

Do you mean that is what it ought to be like if wired correctly, or that is what he would find with it incorrectly wired as shown in the photo?

 

[D_Hailsham]

The correct wiring is:

1 - Live from programmer CH ON terminal
2. Neutral
3. Switched live usually to motorized valve, which turns the boiler on via a microswitch. (I was simplifying things in my last post as there are several ways a boiler can be switched on.)

 

[Ackoman]

The correct wiring is:

1 - Live from programmer CH ON terminal
2. Neutral
3. Switched live usually to motorized valve, which turns the boiler on via a microswitch. (I was simplifying things in my last post as there are several ways a boiler can be switched on.)

Ok - I asked because my thermostat is wired exactly as the one in the picture (well sort of - Term 2 is blue, Term 3 is red and Term 1 is yellow). Term 1 is at 230V when the thermo is set to zero, which implies to me that whoever wired it has connected yellow to the programmer's CH ON terminal and is using red as the switched live. Wouldn't these be better the other way around?

 

[AGAS]

Ok - I asked because my thermostat is wired exactly as the one in the picture (well sort of - Term 2 is blue, Term 3 is red and Term 1 is yellow). Term 1 is at 230V when the thermo is set to zero, which implies to me that whoever wired it has connected yellow to the programmer's CH ON terminal and is using red as the switched live. Wouldn't these be better the other way around?

don't worry about the colours just worry about where the wires are connected too , annoying i know but we've got to live with what we've got until you/your plumber changes it.