i've got an old landis & gyr thermostat which i wanted to replace with an Horstmann HRT2 i brought.
the problem is the wiring!! the landis & gyr thermostat has 3 terminals labelled 2 3 1 in that order. red to 1, black to 2 and nothing in 3. with a earth on the inner case.
The HRT2 has 4...