Fitting honeywell BDR91 with only common and N/O wires possible?

[Drogen24]

I currently have a danfoss tp5000 at the bottom of three floors that controls the entire house. It's terribly inefficient and leaves most rooms freezing whilst one or 2 are unbearably hot so in looking at a smart TRV system and settled in the evohome.
What is currently connected is the danfoss straight to the boiler (have never been able to find any relays or additional thermostats) via a common wire and N/O wire as shown in the picture and there is a blue sleeved, black wire and a neutral terminated behind the wall.

Is this sufficient for the evohome controller, or does it need an additional permenant 230v adding?

Thanks in advance

Edit: if it's relevant, it's a combo boiler I'm connecting to

 

[stem]

As you have figured, the existing thermostat is battery operated and so doesn't have a 230V supply provided for it. The BDR91 is mains powered so yes, will require a 230V mains supply. Which should come from the same 3A fused connection unit as the rest of the heating system.

Remember though the BDR91 is a receiver / relay box, so wouldn't normally be out on show. The usual way to install a BDR91 to a system like yours, would be to find the origin of the wires that go to the existing thermostat. [Either a wiring centre / junction box, or often direct to the boiler itself in the case of a combi. Be careful though the terminals of some boilers should only be accessed by a Gas Safe engineer as they form part of the sealed combustion chamber] The BDR91 is then mounted there out of the way and connected directly to the terminals in place of the wires currently going to the room thermostat. The connection to the 230V supply can then be made at the same point.

 

[Drogen24]

Remember though the BDR91 is a receiver / relay box, so wouldn't normally be out on show. The usual way to install a BDR91 to a system like yours, would be to find the origin of the wires that go to the existing thermostat. [Either a wiring centre / junction box, or often direct to the boiler itself in the case of a combi. Be careful though the terminals of some boilers should only be accessed by a Gas Safe engineer as they form part of the sealed combustion chamber] The BDR91 is then mounted there out of the way and connected directly to the terminals in place of the wires currently going to the room thermostat. The connection to the 230V supply can then be made at the same point.

Thanks for the reply. So to clarify what I'd want to have done by a gas safe engineer, I'd need the BDR91 connecting to the boiler somewhere, probably in the cupboard container the boiler, and the Tp5000 will become defunct as there is no replacement for it in the evohome system?

 

[stem]

If you can trace the wires back from the thermostat and identify which cable it is at the boiler end (assuming that's where it does go) you may be able reroute the existing cable to the new location of the BDR without opening the boiler casing, and pick up the 230V from the fused connection unit / isolator which is usually next to the boiler.

Some boilers you can get to the wiring terminals without opening up the sealed chamber, but not all. If you post back the make / model of your boiler then one of the Gas Safe guys should be able to confirm which yours is.

And yes the BDR takes over the function now done by the room thermostat.

There are only two wires visible at the thermostat in your photo, but there may be a blue hidden wire from the same cable. If the brown wire is a 230V live (some boilers can be wired to use 24v switching instead of 230V. However, the brown sleeve on the grey wire does suggest yours is 230V) it maybe possible to use the spare blue wire to provide the missing neutral and then you would have 230V at the point where the existing thermostat is without having to install another cable.

 

[Drogen24]

There are only two wires visible at the thermostat in your photo, but there may be a blue hidden wire from the same cable. If the brown wire is a 230V live (some boilers can be wired to use 24v switching instead of 230V. However, the brown sleeve on the grey wire does suggest yours is 230V) it maybe possible to use the spare blue wire to provide the missing neutral and then you would have 230V at the point where the existing thermostat is without having to install another cable.

Yes, there is a blue sleeved wire behind the wall along with an earth and your comment about the brown sleeve hogged my memory of changing multiple light fixtures and they all had these grey wires with brown sleeves for the live, electrician the wired the house must not have wanted to pay extra for properly coloured wires.
So I have everything I need to fir the BDR91 in the place that's currently occupied by the danfoss?

 

[stem]

Provided that you can:

1. Confirm that the brown wire is actually a 230V live, which is easy to check with a multimeter, and
2. Find the other end of the blue wire and attach it to a neutral associated with the boilers electrical supply.

Once that is done:

Blue wire (N) goes to BDR N
Brown wire (L) goes to BDR left L terminal
Grey wire (S/L) goes to BDR B
Add a link between BDR right L terminal and A

 

[CBW]

@stem - the thermostat rating is 230Vac switching only

@Drogen24 - in answer to your question (stem has kind of answered it), yes it’s possible to do it Com and No as it’s just a simple switch, battery operated.

 

[stem]

@stem - the thermostat rating is 230Vac switching only

The contacts are rated at 230V, but it's only a relay switch, so nothing to stop them being used with 24v as they sometimes are. However, it looks like it will be 230V in this case as someone has gone to the trouble of fitting a brown sleeve to the grey wire.

 

[CBW]

The contacts are rated at 230V, but it's only a relay switch, so nothing to stop them being used with 24v as they sometimes are.

Ahh, wasn’t aware, so thank you

 

[Drogen24]

Provided that you can:

1. Confirm that the brown wire is actually a 230V live, which is easy to check with a multimeter, and
2. Find the other end of the blue wire and attach it to a neutral associated with the boilers electrical supply.

Once that is done:

Blue wire (N) goes to BDR N
Brown wire (L) goes to BDR left L terminal
Grey wire (S/L) goes to BDR B
Add a link between BDR right L terminal and A

The wire going to common is 119V and there is no voltage when tested on the brown sleeved wire. That doesn't seem correct....

 

[CBW]

What testing equipment are you using, and where/what are you testing?

 

[stem]

Well the second part sounds reasonable.

there is no voltage when tested on the brown sleeved wire.

But as @CBW the actual brown wire should be 230V when tested against a known actual neutral, or earth. The faceplate screw of a nearby light switch or socket often works if there isn't anything else handy.

 

[Drogen24]

I'm using a multimeter, I had the other terminal against the mounting bracket of a nearby radiator although that wasn't earthed itself so I'll try again with a light switch and report back!

 

[ianmcd]

A rad mounting bracket wont work unless it has an individual earth connection

 

[Drogen24]

240v when connected grounded on the light switch, perfect.
Got there eventually, thanks both for the pointers