Evohome Y Plan with wireless boiler relay?

[Ijwoo1]

Hi, I'm hoping someone can help or at least confirm my understanding.

I'm about to install evohome in an existing Y plan system. The standard configuration shown on Fig.3 on page 43 of the installation manual (Wiring diagram P.47, Fig.10) uses two wireless BDR91's to control the 3-port zone valve, with the boiler and pump fired by the DHW relay and/or the orange from the mid-valve end-switch. In other words, the standard configuration for a Y Plan does not use a boiler relay.

My only concern with that is in the absence of a boiler relay I wont be able to tweak the cycle time/on time of the boiler and it seems that some people have had issues with this set up, specifically with the proportional short cycling of the boiler when temperatures are near the set points.

So how to install a BDR91 boiler relay in a Y plan system to get full control of the boiler? Possibly 3 options, but I'm finding the apparent options confusing and contradictory.

1. P.47 says "Y Plan: Three-port Mid position valve with a wired boiler - If a wireless boiler relay is used the Orange and feed to pump and bolier are not required". This suggests you can add a 3rd BDR91 as a boiler relay in the evohome set up, but this is specifically contradicted in this post:Post #50
2. Fig 4, Page 43 shows a 3 port zone valve (V4073) being used in a S Plan Minus configuration, with a DHW relay and a boiler relay. This seems to forgo control of the HTG port by leaving it permanently open, relying on TRVs and a bypass to control heating of the radiators. At least I think this is what Fig.4 is showing? But I cannot find the wiring diagram for this, although a suggestion is made in this post: Post #47
3. Some other way to achieve the Fig.4 set up, by appropriate control of the White and Grey wires on the V4073 similar to the suggestion in this post: #47 but without permanently leaving the HTG port open, although I haven't got my head around this yet, I just sense there should be a smart way to do this.

Or am I over thinking this? Should I just accept that I don't need to control the boiler cycle time etc?

Thanks in advance for help

[Ijwoo1]

I'm replying to my own post so I'm not sure if I hit the nail on the head with my original post and there aren't straight answers or people were too polite to say "RTFM". Anyway, FWIW I think the official documentation and online training leave a lot to be desired but for anyone stumbling upon this in the future I ended up with option (3) from my original post, electing to use just two BDR91 relays. One as a boiler relay and the other as a DHW "Hot Water Storage" actuator in combination with a CS92 Cylinder tank sensor. The Hot Water is set up to use a "Hot Water Only Valve" in the Evo home Hot Water configuration.

I'm using an Arduino based custom controller that controls the Mid-valve's White and Grey wires based on the state of the Pump, which is fed by the boiler and the DHW BDR91 relay. I think it's overkill and I suspect Post #47 that I referred to above would achieve the same result and any concern about the motor being powered for extended periods are unfounded. The synchronous motor in the valve consumes minimal power so wont be as susceptible to burn out as a traditional motor.

For the moment everything seems to be working as expected, albeit after a few attempts at rebinding etc. For the moment I've left the Boiler parameters at their default, so unless I find a problem with the 1 minute short cycling of the boiler I could have just gone with the standard Y-Plan configuration, forgoing the boiler relay and the effort of constructing the custom valve controller!

My thanks to the evohomeshop.co.uk for good pricing and quick delivery. I'm hoping it's OK to mention them as they appear to be sponsors of this site?

[The EVOHOME Shop]

My thanks to the evohomeshop.co.uk for good pricing and quick delivery. I'm hoping it's OK to mention them as they appear to be sponsors of this site?

Sorry for not seeing your post earlier, November and December have been just crazy so has limited my time to help out on here.

I am in the process of doing some guides and videos on our website which will cover the basic setups and some of the advanced things you can do with evohome. Although it is possible in the evohome Controllers INSTALLATION MENU, we are told by Honeywell you cannot use a 3rd BDR91 in an S or Y Plan situation as a Boiler Control Relay as it will cause conflicts (random firing of the Boiler Control Relay), which I believe there are several people on here who have experienced this.

When you have HR92's on all radiators, you can wire the 3 Port Motorised Zone Valve to open to heating side permanently (very much like removing the heating motorised zone valve on an S Plan system) and then use the Boiler Control Relay for the switched live demand.

I hope that helps and as you have purchased your system from us you can email me on [email protected] if you require 1 to 1 on this.

I hope that helps.

Richard