Central heating thermostat replcament - 2 wire/3 wire confusion!

[parham1975]

Hi there,

Can anyone help me - I would like to replcae a 15 year old Potterton thermostat in my house. When I opened the thermostat up I found 3 wires: L, N and a mysterious 'H'. These go to terminals labelled TP1, TP2 and TP3 repectivly.

The thing is the new thermomstat I purchased (Danfoss RMT-230) has 4 terminals but the instructions only shows how to wire the L and N. What do I do with the 'H' wire and what is this mystery wire for??

Any help would be most appreciated!

Thanks Steve

[Phil Anthropist]

First paragraph (Thermostats and TRVs) may help:

The following is a different brand but explains that the 4th terminal isn't used.

[Steve]

Thanks for the information Phil.

So I have 2 options if I understand this (which may be doubtful!).

1. Connect L wire to terminal 1 and N to terminal 2. Presumably I just tape up the 'H' wire. If I do this then the resistor/accelerator is not used.

1. Connect L to terminal 1. Connect N to terminal 4 and H to terminal

1. Then the accelerstor/resistor gets used.

Is that correct? and is 2. th better choice?

Thank you Steve

[Phil Anthropist]

If you are referring to the terminals shown for the Horstmann thermostat, T2 is not used. L wire connects to T1 and N wire connects to T4. H wire if used connects to T3. Your option 2 would be the best choice apart from H wire should go to T3 and not T2.

[ARWadsworth]

shows you how to wire it up.

Adam