Evohome wiring

[doni]

Hi,

I've just purchased evohome and am getting my head round the wiring required. At the moment I have a combi boiler driving to heating zones, where zone-1 is for UFH in the kitchen and zone-2 is the radiators in the rest of the house. This is in a S-Plan configuration with 2x2-port valves isolating each zone.

I've attached the existing wiring diagram, and a diagram which shows the new setup with evohome. The 2-port valve for the radiators will be disconnected from power and permanently latched open, leaving just the 2-port valve for the UFH.

Does the wiring diagram look correct. It seems simple enough, just want to make sure that I'm not missing anything?
Thanks,
Don

Existing wiring Existing Wiring.jpg
Evohome wiring new-evohome.jpg

[Little Tinker]

Assuming you have HR92 valve heads throughout then I think it'll work, but is mixing up two concepts.

If you simply brought the relays to positions 8 and 10 while leaving valve wiring as now then each valve could open under demand control and fire the boiler when needed.

If you want to use what you call the radiator relay in boiler control mode so that it can modulate firing then I think you'd want to also disconnect the UFH valve from boiler supply / return so that it can't also fire boiler.

I'm heading towards a similar setup and think I'll aim for second option. However I haven't set this up yet and do remain a bit unsure how certain options for relay and zone pairing are configured.

[g6ejd]

Does not look correct to me, the BDR91 need a permanent supply also the valve needs permanent supply with contacts wired accordingly. Suggest you look at the valve wiring for amber nd grey which are changeover contacts. If the BDR91's have switched power how do you intend to control them?

The BDR91 documentation has an S-Plan wiring arrangement which you need to merge with your system.

[doni]

Thanks little tinker and g6ejd for your feedback - this has been very helpful!

If you simply brought the relays to positions 8 and 10 while leaving valve wiring as now then each valve could open under demand control and fire the boiler when needed.

The radiators will all be controlled by HR92's (with the exception of bathroom towel rails). The UFH is a single zone and is switched enabled through the second valve - this valve needs to remain in the new setup. I'd originally been told that evohome could only drive one valve, but actually re-looking at the wiring, the two BDR91's just fit straight into the existing setup as you say - routing both to 8 and 10. It was in my face the whole time and I was just working under an assumption!

If the BDR91's have switched power how do you intend to control them?

That's a fault on my diagram. The LS and LR are Live Supply and Live Return from the boiler which would have gone to a wired stat at some point in time. The LS is permanently live and the LR is the switched live (the acronyms are confusing!).

[DBMandrake]

I've just purchased evohome and am getting my head round the wiring required. At the moment I have a combi boiler driving to heating zones, where zone-1 is for UFH in the kitchen and zone-2 is the radiators in the rest of the house. This is in a S-Plan configuration with 2x2-port valves isolating each zone.

Before answering your questions something needs to be cleared up - you seem to be confused about whether you have a Combi boiler or a System boiler with an S-Plan system - you won't have both at the same time... so do you have a hot water cylinder or not ? If you do you have S-Plan, if you don't, you have a Combi boiler. (Instant heat hot water)

If you have a hot water cylinder and S-Plan configuration you need the Evohome hot water kit, (CS92 temperature sensor and additional BDR91 relay) if you have a Combi boiler you don't need the hot water kit.

Also, exactly what evohome kit did you get and how many BDR91's do you have and did you get any wall mount temperature sensors ?

What currently controls the temperature in the zone with UFH - does it have its own wall stat in the old system and are you keeping that or trying to replace that with an Evohome wall stat ?

[doni]

Existing system is combi boiler (no hot water tank) and two heating zones. The first zone is UFH in the kitchen, the second zone is the old part of the house which (currently) has thermostatically controlled radiators. We have two wireless wall stats - one for each zone. When a wall stat calls for heat, it opens the corresponding valve and tells the boiler to heat.

The Evohome home system that I've just bought is HR92's for all of the radiators (except towel rails), two BDR91's (one for the radiator zone, and one for the UFH zone), a wifi connected controller, and a T87RF thermostat for the UFH zone.

[DBMandrake]

Ok thanks, that explains the situation quite clearly.

In that case I'd make the following suggestions. This is not the only possible way that you could configure it, and I have not used UFH before, but it makes the most sense to me.

You need one BDR91 to control the UFH zone in your kitchen, so you would connect this to your UFH zone valve. You would create a zone for the kitchen and bind this BDR91 as a "zone valve" actuator within the Kitchen zone. You would then bind the T87RF as the temperature sensor for the Kitchen zone. So far, so good.

Where it will get a little confusing is what to do with your other zone valve and boiler control and whether or not to use the orange and grey wires on your zone valves to fire the boiler or not.

You can't just bind the second BDR91 as an "all zones except the Kitchen" relay. This BDR91 will have to be configured as a "boiler control" relay, which will turn on when any zone requires heat, whether HR92 controlled or UFH.

The question is where to connect this boiler control relay. The easiest least wiring change approach would be to connect it to your radiator zone valve for the rest of the house.

This will work but in a roundabout way, because this zone valve will be opened for both HR92 demand and UFH demand, (since the boiler control relay comes on for any demands) however if there was only UFH demand the zone valve for the rest of the house would still be opened - but because all the radiators are controlled by HR92's this doesn't matter as they will be closed and there would be no flow except for your UFH.

The other way to do it would be to connect the boiler control BDR91 directly to the boiler and disconnect the orange and grey control wires from both zone valves so that the zone valves aren't trying to fire the boiler. Then either latch open your radiator zone valve or connect it to something like pump power so that it will open whenever the pump is running. Again, the zone valve will either be always open or open when the pump is on, meaning that it will be open when there is only UFH demand, but because the HR92's will be closed there won't be any flow through the radiators.

An advantage to this approach instead of continuing to use the orange and grey wires of the zone valves is that you don't loose 15 seconds of boiler run time in each 10 minute TPI cycle (waiting for the zone valve to open and activate its switch) and the pump overrun during TPI cycles would be able to flow through the radiators instead of being forced through the automatic bypass valve. (You have an ABV, right ?)

So it's up to you which approach sounds best to you but both should work. I would tend to go for the option of having the relay directly control the boiler and disconnect the orange and grey wires on the zone valves, latch open the radiator zone valve or wire it to pump power.

[doni]

@DBMandrake - thank you! That's cleared the fog away from my head about why the radiator two port valve had to be latched open.

I'd do have an ABV - although I will come back at some point and ask how to set it :-)

[doni]

First some feedback - I installed everything over the weekend. Was relatively straight-forward and only took a couple of hours. Thank you everybody for your help!

As an aside, does anybody use the evohome touchscreen as a temperature sensor for any of their zones? At the moment, the Kitchen uses a T87RF as it's temperature sensor. However one of my zones is struggling a little because the HR92 is behind a curtain, so I'm considering moving the T87RF to this zone, and having the evohome touchscreen act as the sensor for the Kitchen.

[Bazinga]

We use our evohome controller as a zone sensor for our lounge. We tried using an offset compensation on an HR82, but it was always needing to be changed depending if the sun was heating the room or not. I changed the temperature sensor to use the controller and it's close to perfect now. The temperature at another thermometer varies from the evohome controller by at most +/- 0.2C now. I had to apply an offset of -0.7C to the temperature measured by the controller (you'll find it in the installation settings). I think that it was DBMandrake who pointed out that this is likely because of heat generated by the charging circuits within the controller. If you do decide to use the controller as a zone sensor, then try to avoid picking it up from its cradle. The heat from your hand will send the temperatures soaring. The desktop stand is quite stable on ours and we make all adjustments with it on the stand.