Replacing mech room thermostat with a remote 240v one HELP!

[M@H]

Hi Chaps,

Hoping you can help me with a bit of guidance.

I have a "normal" mechanical room thermostat in my house and wish to replace it with a remote one. I have purchased a remote one (siemens RDH10RF/SET ) which has a 240v feed for its operation but does "volt free" switching too.

The issue comes in that the existing mechanical stat has three wires connecting it back to the boiler controller - one from a heater control valve (S plan), one that goes to the heating/hot water switch at the boiler, and one that goes to the neutral line across the control connectors (picture here http://www.esse.com/support/cookers/installation-i... page 13 S plan)

..and the new Siemens thermostat has three connections labelled L1 (N.O call for heat ON), LX (common), and L2 (N.C Heating satisfied OFF) but a comment saying that for "volt free" connections L2 is not normally used and for 240v switching to link L and LX (L being the Live feed from a 240v source).

I am a bit stuck as to how to wire this one in - can anyone help me?

Many thanks,
Matt.

[Arthur Jackson]

You need to switch the two wires that are left if you IGNORE the neutral.
You will need a live and neutral for the running of the thing and you can use the neutral for that BUT you must have a further PERMANENT live. Neither of those other wires are suitable.

[Rickyy]

Is it just a stat or a programmable stat?

If it is just a stat, wire the receiver with a permanent live supply and a neutral. Then find out which wire is the CH ON from the timer, this is connected to your common (LX I think you said) in the receiver.

Then connect the NO or call for heat from your receiver to the brown wire on your heating zone valve (assuming its a standard 5 wire zone valve and not a sunvic or range type).

If it is a programmable room stat, take your permanent live supply and a neutral to receiver, but link the L terminal to LX and continue as previously stated.

I'm assuming you have a conventional boiler with 2 x 2 ports as you mentioned "S-Plan"?

Volt free switching usually only applies to combination boilers, wear low voltage is used to operate the heating.

[M@H]

Thanks both,

Just to confirm a couple of things I am aware I am going to need an independent 240v supply to run the new stat receiver(its not a programmable thing, just an electronic remote reciver for a mobile room stat) and it is to be attached to my "conventional" boiler which is an Esse range cooker as per the manual above which is for my model (wired S as Plan)

I think I understand from what you are both saying that I only use two of the three wires from my current mechanical stat on the new one, and yes it is a normal zone valve with brown wire. CH ON is currently connection 1 I believe and the brown wire is conneciton 3, so those two wires become LX and L1 respectively.

What about LX 2 though, if I am not "volt free" then surely it needs something?

Many thanks again,
Matt.

[Rickyy]

M@H said:

Thanks both,

Just to confirm a couple of things I am aware I am going to need an independent 240v supply to run the new stat receiver(its not a programmable thing, just an electronic remote reciver for a mobile room stat) and it is to be attached to my "conventional" boiler which is an Esse range cooker as per the manual above which is for my model (wired S as Plan)

I think I understand from what you are both saying that I only use two of the three wires from my current mechanical stat on the new one, and yes it is a normal zone valve with brown wire. CH ON is currently connection 1 I believe and the brown wire is conneciton 3, so those two wires become LX and L1 respectively.

What about LX 2 though, if I am not "volt free" then surely it needs something?

Many thanks again,
Matt.

Yes, you will need a permanent 240v supply for the receiver. The grey wire on your zone valves will be connected to a permanent supply, so you can connect to that and a neutral obviously.

Yes, existing 1 and 3 become LX and L1.

The term volt free is a bit confusing. What it means is that the switching part of the stat (LX, L1 and L2) is separate to the 240v supply part of the stat. As a lot of combi boilers use very low voltage to switch the heating on and off.

L2 will not be needed, it becomes live when the thermostat is satisfied. I believe certain set-ups require a satisfied signal, but I doubt that your set-up will.

[M@H]

Excellent stuff, thank you very much

[M@H]

All wired in and works beautifully - that was the best £20 I have spent in ages

Thanks again