Wiring for a Honeywell dial thermostat

[DIYspanner]

From what I've read, terminal 1 in the Honeywell thermostat should be permanent live and terminal 3 should be switched live.

My multimeter says they are the wrong way round. I've looked at the isolator switch wiring for the Vaillant Turbomax Vuw combi boiler. There's a 4 core into the boiler.

 

[CBW]

The 120vac is odd, are you testing correctly between neutral or cpc/earth? 120vac is usually when you test between Live and switched. At the Honeywell test between 1 and 2 without demand, you should get around 230vac. Between 2 and 3 without demand should be 0vac and with demand should change to approx 230vac.

 

[DIYspanner]

The 120vac is odd, are you testing correctly between neutral or cpc/earth? 120vac is usually when you test between Live and switched. At the Honeywell test between 1 and 2 without demand, you should get around 230vac. Between 2 and 3 without demand should be 0vac and with demand should change to approx 230vac.

I concur with what you say based on what I've researched on YT. It seems to me that the connections for the thermostat at the boiler need checking.

 

[DIYspanner]

This picture of the boiler's install manual indicates the relevant terminals on PCB so I'd need to ascertain which connect to terminals 1 and 3 on the Honeywell T6360B.

 

[CBW]

This picture of the boiler's install manual indicates the relevant terminals on PCB so I'd need to ascertain which connect to terminals 1 and 3 on the Honeywell T6360B.

It should be 3 (common/live) out from Vaillant to 1 on Honeywell
3 out (switch live) from Honeywell to Vaillant.

What is it you’re trying to achieve?

 

[DIYspanner]

What is it you’re trying to achieve?

Basically I want the Honeywell and Vaillant wired correctly.

Is Vaillant 4 or 5 the switch live?
Presumably the remaining of three being the neutral!

 

[DIYspanner]

This gives the wiring info. p20

Is it necessary to take the permanent live and neutral for the Honeywell from the combi's pcb terminals?
Could they be taken from the switched side of the isolator switch?

 

[CBW]

Vaillant 5 is neutral. 3 permanent live 4 switch live, which is what I said in post 5 minus the neutral

 

[DP]

Control wiring is a walk in the park.
If it is beyond ones reach after explanation, leave well alone.
Not the first programmer or a pcb been blown up by the uninitiated

 

[DIYspanner]

I found the issue having looking at the Vaillant pcb !

Honeywell 3 is connected to Vaillant 3
Honeywell 1 is connected to Vaillant 4

The neutral in the Honeywell 2 is connected to the switched side of the isolator.

 

[DIYspanner]

Why should there be 120v between Vaillant 4 (SL) and neutral at the Honeywell when the wire is pulled out of its terminal?

Can the thermostatic circuit in the Vaillant work correctly without the neutral connected to its terminal 5?

 

[CBW]

Switch live only becomes 230/240Vac when it’s fully operational, but I think you should only have 0-15vac when no call for heat

 

[DIYspanner]

Fault identified!

The 3 core + earth cable run between the boiler and wall thermostat.
Using the blue as neutral, with all wires disconnected at the Honeywell, there's around 120vac between the unconnected wire/neutral and unconnected wire/connected wire at the other end when I connect to the mains supply for the isolator switch. So it seems to be an insulation problem on the 3 core.

There's no other visible device on any wall that could be connected be between the Vaillant and the Honeywell so rather than run a fresh cable, I believe a wifi room thermostat is the solution.

By the way, I removed the two wires from 3 and 4 on the Vaillant. 3 is 240vac and 4 is 0vac so all good there.

 

[DIYspanner]

The Honeywell T3r seems a good choice.

 

[CBW]

The Honeywell T3r seems a good choice.

Not a bad thermostat, fitted quite a few. Expensive and over engineered imo though.