Worcester Bosch Combi Room Thermostat Replacement

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2 Oct 2022
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Hi All,

I've got a Worcester Bosch Greenstar 30Si combi boiler and I'm trying to replace the room thermostat which has a faulty display.

The faulty thermostat is a DT10RF optimiser which is discontinued so I purchased a Comfort 2 RF which is supposed to be the equivalent replacement.

It should be a simple case of swapping out the receiver on the boiler which was easy enough but the new receiver doesn't power up with the boiler - the LED doesn't come on and the room thermostat shows fault A21 indicating it can't connect to the receiver.

The old receiver used a ribbon cable to connect to the boiler whereas the new one uses a 3 pin EMS bus connector but the installation guides for the boiler and thermostat suggest this should just work.

Has anybody successfully made this change? Is there another step required in the boiler to turn on the EMS bus connector?

Thanks.
 
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