Faulty underfloor heating thermostat but new one has different terminal labels - help please!

[M1AK]

Hi all,

My underfloor heating, ever since installed has never worked and I have a fault with the thermostat too (it randomly stops working and randomly fires the heating on, so I know the heating element and power is fine). To rule the issue out I bought a replacement thermostat however the connections vary slightly, and I need some assistance if someone could kindly help.

the old thermostat has

L - with a live cable on it
N - with two neutral cables on it
COM - with a short cable running in between L and COM terminals
NO - with a underfloor heating cable
5&6 with a thin white and brown cable, from the sensor.

The new thermostat has:
L
N
N1
L1
5&6

I can obviously work out L, N 5 & 6 as its like for like. I don't know whether the short cable runs between L and N1 or L and L1 and if the underfloor heating cable goes to L1 or N1.

Appreciate if someone in the know could kindly advise. Thanks in advance

 

[EFLImpudence]

Hi all,

My underfloor heating, ever since installed has never worked and I have a fault with the thermostat too (it randomly stops working and randomly fires the heating on, so I know the heating element and power is fine). To rule the issue out I bought a replacement thermostat however the connections vary slightly, and I need some assistance if someone could kindly help.

the old thermostat has

L - with a live cable on it
N - with two neutral cables on it
COM - with a short cable running in between L and COM terminals
NO - with a underfloor heating cable
5&6 with a thin white and brown cable, from the sensor.

The new thermostat has:
L
N
N1
L1
5&6

L - Supply L
N - Supply N
N1 - outgoing UFH N
L1 - outgoing UFH L
5 & 6

No link wire necessary.

I don't know whether the short cable runs between L and N1 or L and L1

Neither.

and if the underfloor heating cable goes to L1 or N1.

Both.

 

[Ragnar_AT]

The old thermostat probably has another unused relay contact that could be connected to a terminal labelled NC. Depending on the state of the thermostat, the relay connects COM either to the NO or the NC terminal. The NC would be used for controlling an air conditioner. Since the relay contact are completely independent of the supply, you need the link from L to COM. The advantage of this is that you could use the relay for all sorts of things not referenced to the mains, like switching 12 V DC or any other voltage.

The new thermostat has a factory link from the supply to the relay so it can only be used for mains AC but is easier to wire.

 

[M1AK]

Thanks for the replies. I have attached pictures. The one with wires is of my existing thermostat and

The old thermostat probably has another unused relay contact that could be connected to a terminal labelled NC. Depending on the state of the thermostat, the relay connects COM either to the NO or the NC terminal. The NC would be used for controlling an air conditioner. Since the relay contact are completely independent of the supply, you need the link from L to COM. The advantage of this is that you could use the relay for all sorts of things not referenced to the mains, like switching 12 V DC or any other voltage.

The new thermostat has a factory link from the supply to the relay so it can only be used for mains AC but is easier to wire.

There is no NC terminal. I'll post up pictures to show where I am stuck.

 

[M1AK]

Thanks for the replies, but unfortunately I am still a little confused on the two cables. I have attached two pictures to add some context of the existing wiring of our electric UFH.

Currently it is wired like this (see image of thermostat with wires) and I am trying to transfer it to the second picture.

L and N I can work out as can I of the UFH sensor. But as shown I have a short bridging wire from 'L' to 'COM' and 'NO' has a underfloor heating wire. I also have two wires going to N.

I can replicate this to the new thermostat but I don't know where COM and NO go in the new thermostat, as its labelled as N1 and L1.

 

[Ragnar_AT]

L goes to L
One of the blues from N goes to N, the other to N1
NO goes to L1

It probably doesn’t matter which blue wire goes where but I‘d try to see which one is part of a cable with the brown that‘s connected to L. This blue wire goes to N.

The short link goes into the bin, it’s already built into the new thermostat.

 

[M1AK]

L goes to L
One of the blues from N goes to N, the other to N1
NO goes to L1

It probably doesn’t matter which blue wire goes where but I‘d try to see which one is part of a cable with the brown that‘s connected to L. This blue wire goes to N.

The short link goes into the bin, it’s already built into the new thermostat.

Thank you for your help, appreciated.

I was thinking that but wasn't sure and better to be sure. I've noticed one of the blue cables going to N has a little grey insulating tape, which is visible in the pic too, further up. I'm assuming this is part of the UFH cable as someone's tried to distinguish it. But i'll remove the box behind it and see if I can see which blue wire is within the same cable jacket as the brown L, as you suggest. Thank you