Evohome: Hot Water demand switches Central Heating on too.

[jweaver]

A few weeks back changed my Honeywell CM67z to a EvoHome.. I have had many teething problems but am starting to get used to the Nuances of the system.

I have 2xMotorized Vales in my Central heating, but they are wired in parallel.

I have a single BDR91 which opens both valves at the same time and all works nicely.

Last weekend I decided to integrate my Hot Water system into the Evohome and it was pretty straight forwards.. I replaced my 1 channel timer with the BDR91 and installed the Themocouple into the Dry Pocket on my tank and soon got it all bound up.

But then it came to the test and when I triggered the hot water, BOTH BDR91s activated starting opening the central heating and Hot water valves.

To cut a long story short, I believed I found the root of the issue and had the BDR91s "double bound" so I cleared it all out and started again... And I thought I had it working.

But because my tank was hot, I had very little chance to see it in operation, until today when my other 1/2 had a bath, using up much of the water.. Now the tank was down to 12 degrees, I had a good chance to play.

And I found it wasn't fixed.. And I am still getting CH and HW when I only call for HW.

I put all of the heating zones down to 5 degrees so there was no HW demand.. And turned on the heating, and both CH and HW BDR91s activate.. And when I look at "System Info" on the Evohome I can see that I have 100% against "APPLIANCE" and "HOT WATER STORAGE".. So the relays are actually doing what they are told and its the Evohome which is making the demand.

I ahve tried everything.. I have changed every option and re-bound the BDR91s more time that I can remember and the behaviour is constant.. if I create 0% demand for CH.. And then create demand for HW, both the CH and HW calls for heat.. And I am now starting to think I misunderstand how this all works and perhaps this is normal?

I can't see how, as before I had 2 independent "relays" controlling Water and CH.. So I don't know why the Evohome would combine them.. But perhaps there is a reason.

My fingers are crossed the someone can help me as I have run out of ideas and am currently thinking of putting my old timer back.

 

[jweaver]

To be clear.. I have read many posts with similar symptoms to this but the cause is either:

1. Communications Issues to the BDR91s
2. Faulty valves - where the relay closes on the BDR91s but the Valves still create demand.

My case is totally different.. The BDR91s are doing exactly what they are told to do.. But the EvoHome has 100% demand on the CH and HW at he same time, when there is 0% demand on any of zones.

 

[ianmcd]

No it is installed wrong, 2 x zone valves require 2 x single channel BDR91s one for each zone valve

 

[jweaver]

No it is installed wrong, 2 x zone valves require 2 x single channel BDR91s one for each zone valve

No. They are just wired in parallel so just act like one valve... I retrofitted Evohome over my old setup which was basically 2 relays (CM67z Thermostat for CH.. And 1 Channel timer for HW).. the CH relay (CM67z) controlled the 2 valves with no problem... It didn't even care.. It just put mains onto the motor of each and they actuated and the first that triggered its microswitch fired the boiler.

There is no doubt that to make this a 'true' 2 zone setup, would need to BDR91s... For my application they are just wired as one.

Anyway.. The issue here is (was) with the logic on the Evohome and not the Valves/Wiring and after a VERY helpful chat with Honeywell they knew exaclty what the issue is and its fixed.

And basically for a setup like mine you do NOT bind the CH BDR91 to the "APPLIANCE CONTROL".. You just select STORED HOT WATER.. And then 2/3 WAY VALVES... And you bind the 2 BDR91s and the CS92A under the STORED HOT WATER menu.

When it done, APPLIANCE CONTROL should stay as NONE....

I did what they said and it appears to work now.. I can create demand on CH only.. HW only.. And CH/HW and the BDRs operate as I would expect.


So if anyone else has this setup, you do NOT bind a BDR to APPLIANCE CONTROL.. You bind both the CH/HW BDRs under "STORED HOT WATER"...

Terrible design to be honest.. And the lack of documentation is borderline criminal.. But atleast the guy on the phone knew exactly what the issue was.

 

[ianmcd]

For my application they are just wired as one.

tHEN WHAT IS THE POINT OF HAVING TWO ZONE VALVES THEN ? sorry caps lock was on

 

[jweaver]

tHEN WHAT IS THE POINT OF HAVING TWO ZONE VALVES THEN ? sorry caps lock was on

I knew that was coming.. I didn't install the system... The original builders did.. They must have had the idea of a 2 zone house.. But then used the CM67Z stat and HR80UK TRVs to do it in "software"..

Infact the cynic in me goes a bit further.. The house is 12 years old and had many "mod-cons" because the developer wanted to build a "luxury estate".. I wonder if the developer (Barrett) told the plumbers to create the best system they could, and they just threw extra valves in because they had an open cheque book.. There are many things in the house which are uncessary to be honest.. An extra valve is the tip of the iceberg.

So the capability is there to do a 'true' Two Zone setup.. But its not used... And even though there was the option to do it as part of my EvoHome upgrade, whats the point when the 'zones' are created by electronic TRVs at the rads, rather than Motorized valves in the airing cupboard.

So other than a bit of extra complexity and a bit more risk of reliability issues.. There is no problem having 2 vales and its certainly not worth doing anything about if they are there..

 

[ianmcd]

well to do it correctly, either remove or disconnect the CH zone valve electricallly, and manually latch it open and the smart TRVs will take over, it is serving no purpouse whatsoever the way it is, if wired correctly your Honeywell evo home trvs will fire the boiler when required

 

[DP]

BDR is a wireless relay- nothing else
Binding process is incorrect if both BDR boxes are activating.

HW demand should only operate HW MV
CH is under control of smart heads. Smart head calls for head, CH BDR operates And runs the boiler