BDR91 to Hive conversion advice

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Hi all!

Our old thermostat controller isn't working anymore, so we are looking to do a DIY upgrade from the old Honeywell BDR91 to Hive. We would appreciate some advice from the experts on this forum!

We have a "Vaillant EcoTech Pro 28" combi boiler, and I have attached the current BDR91 wiring.

Based on other posts in this forum, I believe we will need to do the following for BRD91->Hive:
  • Left blue wire in N -> N
  • Left brown wire in L -> L
  • Right brown wire in A -> Hive Com,1
  • Right blue wire in B -> Hive heating,3
Does this sound correct? It seems simple, but we are confused about whether we should have some extra earth wiring for the Hive earth tether?

Hive unit we have in mind (I think it is correct?): https://www.amazon.co.uk/Hive-Heating-Thermostat-Professional-Installation/dp/B011B3J6KY/

Please let me know if you have any other questions/advice :)

Best,
JeffyJeff
 

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That is correct. Use a pen to mark the wires before disconnecting, as the left and right set are NOT the same, mixing them up will very likely cause expensive damage.
Power must be disconnected completely before doing anything, usually at a switch adjacent to the boiler. Switching off at the boiler itself is not sufficient.

The earth terminal is for any earth wires that are there, which are probably joined behind the existing BDR91 plate. Or some useless type has cut them off.
 

CBW

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Edited - doesn’t matter now
 
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That is correct. Use a pen to mark the wires before disconnecting, as the left and right set are NOT the same, mixing them up will very likely cause expensive damage.
Power must be disconnected completely before doing anything, usually at a switch adjacent to the boiler. Switching off at the boiler itself is not sufficient.

The earth terminal is for any earth wires that are there, which are probably joined behind the existing BDR91 plate. Or some useless type has cut them off.

If we take off the BDR91 plate and don't see any earthing cables, what do you recommend we do? Just, ignore it?

Thank you so much flameport, this is re-assuring, so I think we will try and give it a go soon!

Best,
JeffyJeff
 
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The Hive doesnt require an earth, the tether is simply there to park any existing wire it does not connect to anything, you will see some posts with L&1 linked, do not do this with your set up, A&B to 1&3 either way roud it wont matter
 
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I’m told Earth is required to maintain continuity

Any fixed wiring that has conductors carrying mains power should have an Earth conductor ( CPC ) even if the appliance(s) it is supplying do not require and Earth.

CPC = Circuit Protection Conductor
 

CBW

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Any fixed wiring that has conductors carrying mains power should have an Earth conductor ( CPC ) even if the appliance(s) it is supplying do not require and Earth.

CPC = Circuit Protection Conductor
Thanks, this is what I’ve been told. So if I’m installing something that is double insulated and has no Earth terminal, if I take 5 core flex, leave cpc in a choc block and connect to Earth on boiler/fcu?
 
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CBW

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This doesn’t make sense to me. It’s double insulated like a hairdryer is, which has no Earth wire, and if a fault occurs, the user is protected. Surely this would be the same to other class 2 appliances? (n) So cpc connected one end the other in a choc block is doing what exactly?
 
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This doesn’t make sense to me.

At some time in the future the system might be changed and the new items may require an Earth.

If a cable is damaged ( nail, screw, rodents teeth ) then having a CPC in that cable increases the likely hood that a protective device ( MCB, RCD ) will operate and remove power from the damaged cable.
 
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CBW

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At some time in the future the system might be changed and the new items may require an Earth.
If this is the case, then surely I can just leave tails of wire at each end left disconnected?
If a cable is damaged ( nail, screw, rodents teeth ) then having a CPC in that cable increases the likely hood that a protective device ( MCB, RCD ) will operate and remove power from the damaged cable.
If the main source it’s connected to, such as the boiler or fcu has a cpc, would this not do this?
 

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No. The CPC has to be at the place where the damage to the cable happens.
I still don’t understand how if it’s not connected to the receiver end (class 2 Double insulated) how under fault conditions it would then go back to source :notworthy:(n) obviously I get if this happened on a fcu to boiler because it’s continuity is in tact.
 
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