Replacing BDR91 with Hive

[deanh]

Hi Guys,

I’m trying to replace my existing BDR91 with hive hot water and heating socket but unsure what goes where, current socket also has switched spur into it as well, any help greatly appreciated.

 

[stem]

I assume by:

I’m trying to replace my existing BDR91 with hive hot water and heating socket

that you mean a Dual Channel Hive with Central heating and Hot Water control abilities, is that correct?

It's also rather an unusual installation because:

1. The C terminal is not normally used by UK heating systems, with very, very rare exceptions. What is the other end of the black wire in C connected to?

2. You mention "Hot Water" but The BDR91 is designed to only control central heating and doesn't have hot water control, so there won't be any wires there relating to the hot water system. A single channel Hive would be a replacement for it. However, If you do have a external hot water storage system connected to your boiler (hot water cylinder). What controls that at the moment?

 

[ericmark]

You show a thermostat (BD91) and a programmer/thermostat (Hive duel channel) they do different things.

I typical central heating has a wiring centre, programmer, and thermostats one for the room temperature and one for the water temperature and a motorised valve/s which control the water flow and act as relays. Some systems have some parts built into the boiler, and we can also combine thermostat with programmer and also make it into a hub to gather info from remote thermostats, often called TRV's or use the return water. Often the wiring is low voltage (230 volt) but it can also be extra low voltage (24 volt) and even with some variable voltage (0 - 48 volt).

Step one is find out what you have, it is a waste of money getting a thermostat which can connect to boiler e-bus if the boiler does not have an excisable e-bus, also pointless buying a 230 volt controller if the boiler needs a volt free type. In the main any motorised valve is 230 volt, there were some odd 24 volt versions, but rare. And inside the motorised valve there is normally a micro switch, so the programmer tells the thermostat it is required, the thermostat tells the motorised valve to open, and the motorised valve tells the boiler to run.

But this can be swapped around where the motorised valve (TRV with electronic head) tells the thermostat/hub what to do, and then the thermostat hub tells boiler what to do. And some of the interconnection can be with radio waves. So today we have to select parts which will work together, and since the boiler is the most expensive part, we select control items to suit the boiler.

 

[deanh]

Hi, my current thermostat only controls the heating and not hot water, but the new hive has both, not that I will use it for hot water anyway and only wish to use this for heating.

 

[stem]

The Hive Dual channel is not a direct replacement for the BDR91. It is configured differently internally. However, the Hive Single channel and BDR91 are the same. Hive single channel has voltage free switching, whilst the dual channel has only 230V switching.

It maybe possible to use the dual channel version, but to advise further we need to know:

1. What is connected to the other end of the black wire in the BDR91 terminal C?

2. There appears to be a link between BDR91 terminals L and A. Is that correct? If so, that does indicate that 230V switching is currently being used. .

 

[RandomGrinch]

2. There appears to be a link between BDR91 terminals L and A. Is that correct? If so, that does indicate that 230V switching is currently being used. .

Definitely!

 

[stem]

OK then, to move the wires for 'like for like' functionality from the BDR91 to Hive would be as below:

Wires in BDR91 N = Hive Dual Channel N (Neutral)
Wires in BDR91 L = Hive Dual Channel L (Live)
Wire in BDR91 B = Hive Dual Channel 4 (Heating on)
Wire in BDR91 C = Hive Dual Channel 2 (Heating off)

The existing link between the BDR's second L and A is made internally by the Hive Dual Channel so it's not needed anymore.

If there isn't a hot water system connected Hive terminals 1 and 3 will be vacant.

I still have concerns about the black wire in BDR terminal C, it will be made live when the Hive switches off the heating. Which will be the same as the BDR does now, so nothing really changes. Except as you can see from the BDR installation manual below terminal C doesn't have a wire in for any of the applications shown.

My concern is what is happening at the other end of the black wire that is becoming 'live' when the heating goes off. It maybe terminated safely at the other end, floating around loose, which could be dangerous, or actually doing something. I don't know.