Central Heating Room Thermostat Wiring Help

25 Oct 2010
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United Kingdom
I need some advice on replacing an old Central Heating thermostat with a new digital Honeywell THR840DUK. The Thermostat controls an Oil fired boiler which provides Hot Water & Central Heating.

The old thermostat I'm replacing is a Potterton PRT100 and is wired as follows.

The wires are Red, Yellow & Blue. (The white colouring is actually paint)

Wiring Diagram for Potterton PRT100

Please can some one advise what wires I need to connect to the new thermostat A B C

Many thanks.
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Old stat

Blue, Terminal 4 = Neutral
Yellow, Terminal 2 = Heat
Red, Terminal 1 = Live

New Stat
Yellow = B
Red = A

As the "Neutral" is not required then isolate the blue wire but do not connect it to A, B or C
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