S Plan with Opentherm setup

[Norfolkboy]

Good morning,

I was wondering if anyone may be able to assist me- My current system is an S Plan design with two Honeywell valves, hot water cylinder and Viessman 100 boiler. Current controls is a Salut IT500 wireless thermostat
Am going to convert to the full Evohome system- Hot water kit, HR92s on all rads, Opentherm Bridge. I am going to manually lock open my CH valve and keep my two towel rails with standard TRVS to allow them to heat up when the hot water is on (The wife will be pleased).
Couple of questions.
Can the BDR for the hot water be swapped over with the wiring in my current controller? But currently valve opens first on the current setup then boiler/Pump- does this need to be re-configured to get the boiler to fire?

Opentherm- This is where i am most confused- will it call for the boiler to fire up? As in the product description it says:
"Wireless OpenTherm Bridge (R8810) is a replacement of the BDR91 Wireless Relay Box".
Therefore to get my boiler on for CH do i need a BGR91 or will the Opentherm do the job?

The online course gives no mention of the Opentherm Bridge in the setup

Any help would be much appreciated
Jon

[HenGus]

The experts will no doubt come back with a more detailed response; however, as I am finding out the embodiment of Opentherm is not without its challenges.

You will need the Honeywell Opentherm low voltage Bridge to connect to the boiler - replacing the CH BDR. In addition, I am told that you will need a Viessmann Hot Water Demand junction box. Without it, when hot water is required, it will only heat the cylinder at the modulated boiler water temperature. The idea is that when hot water is required the boiler kicks in to max temperature for the short time that hot water heating is required. You may have this already.

The bit of your question that I do not understand is the reference to the bathroom towel rails. Surely, if you fit standard TRVs these will be TRV-controlled when CH rather than HW is on?


http://www.viessmann.com/vires/produ...VMA00001_1.PDF

http://www.viessmann-us.com/content/....file/file.pdf

[Norfolkboy]

Thanks HenGus, i have picked up the Viessman hot water demand box and also the opentherm bridge. I have just installed the bridge on the boiler and pressing the button activated the boiler- therefore if i latch open my CH valve, then that side of my heating is sorted as the controller will control the opentherm? is it that simple??

Im happy for the towel rails to always be hot even if its HW calling for Heat rather than a zone in the house- i can control the temp with the TRVS and in the summer i could just switch those rads off- i may fit HR92s but will see how it goes.

Thaks for the fast response

[HenGus]

i will leave it to others to advise on wiring etc.

Your towel rails will only be on when a HR92 is demanding heat if they are connected to the CH system.

[DBMandrake]

i will leave it to others to advise on wiring etc.

Your towel rails will only be on when a HR92 is demanding heat if they are connected to the CH system.

In his first post he said he was locking open the CH zone valve - in which case the towel rails will heat up with hot water demand as well, although possibly not much if there is no balancing valve in the flow to the cylinder, as the cylinder will tend to steal most of the flow without one.

Personally I'm not keen on that approach - I want to be able to get hot water in the summer without any wasted heat in the bathroom, and prefer to schedule my bathroom radiator with an HR92 as well, but I know a lot of people like their towel rails to get hot whenever the boiler is running...

[HenGus]

In his first post he said he was locking open the CH zone valve - in which case the towel rails will heat up with hot water demand as well, although possibly not much if there is no balancing valve in the flow to the cylinder, as the cylinder will tend to steal most of the flow without one.

Personally I'm not keen on that approach - I want to be able to get hot water in the summer without any wasted heat in the bathroom, and prefer to schedule my bathroom radiator with an HR92 as well, but I know a lot of people like their towel rails to get hot whenever the boiler is running...

Spot on. My thinking is conditioned by my conventional 'S' Plan arrangement with the 2 motorised valves still functioning.