Replace my ancient Honeywell mechanical thermostat with a Honeywell T3R

Peejay · Dec 13, 2022

I would like to replace my ancient Honeywell mechanical thermostat with a Honeywell T3R PROGRAMMABLE THERMOSTAT

I have three wires in the old thermostat. Please see the first three photos.

1 Red
3 Yellow
2 Blue

are these

1 Live
3 Live return (Switched)
2 Neutral

Could I configure it as in the combi boiler option with a separate power supply and connect Red to A and Yellow to B as the Red wire is not always live and Blue terminated/Isolated (Not used)

or

Option 1 and leave the controller, which is a Seimens RWB29 heating on constant and control it from the T3R

Red to L and L linked to A
Yellow to B
Blue terminated/Isolated (Not used)

Many thanks for your time

Lucien Nunes · Dec 14, 2022

are these

1 Live
3 Live return (Switched)
2 Neutral

Yes, that seems correct.

Could I configure it as in the combi boiler option with a separate power supply and connect Red to A and Yellow to B as the Red wire is not always live and Blue terminated/Isolated (Not used)

That would work. But be sure to put a notice that the relay unit is powered from two separate supplies, both of which must be isolated before undertaking any work. TBH this would be a bit of an odd setup though, in a nornal domestic installation.

Option 1 and leave the controller, which is a Seimens RWB29 heating on constant and control it from the T3R

Red to L and L linked to A
Yellow to B

So far so good but the neutral would still need to be connected to power the T3R.

Can you access the wiring centre, or the connections at the programmer, to reconnect the red as a permanent feed independent of the programmer?

Replace my ancient Honeywell mechanical thermostat with a Honeywell T3R

Peejay

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Lucien Nunes

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