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Problem with a thermostat replacement

Postby steve.atkinson » Sun Nov 16, 2008 10:55 pm

I recently replaced an old Sunvic tlm (rotary type) thermostat with a TLX 7501 digital, however when I found three wires on the old thermostat, i presumed that the neutral wire (blue) wired to the ON terminal and the live (red) to the COM terminal leaving the yellow to be wired into the remaining terminal. however the unit shorted out and now the heating will not work. I have checked the main fuse box but nothing has blown. Can anyone tell me where to the fault or fuse may lie? :(
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Simply Build It

Postby plumbbob » Mon Nov 17, 2008 9:16 pm

The red should be connected to the "com" terminal and the yellow connects to the "on" contact. The blue neutral is not required when connected to digital thermostats.

With the power off, disconnect it and join the red and yellow wires together. Switch the power back on and see if the heating fires up.

Apart from the main fuse box, the only other fuse is in the switched fused spur where the heating system is joined to the house wiring and will have a normal "plug" type fuse.

If all the fuses are ok, you may have damaged various components in the system, but the most likely will be the new stat has been destroyed.
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