Evohome - opentherm and Vokera

[Bilabong007]

Hi,

Just purchased an evohome system with the opentherm interface (R8810A).

When i wire it up to my Vokera vision 30c, it sets the DHW temp to 38°C and there is no way to control this using the evohome controller?

Any ideas, im stumped and back to using a BDR91 relay for now or the missus will kill me as the shower is really a bit too cold even for a scotsman

Cheers

Graeme

 

[muggles]

Does this help? https://ensupport.getconnected.hone...emperature-on-an-evohome-Wi-Fi?language=en_US

If not then @vulcancontinental may know the answer

 

[Bilabong007]

Hi,
The option seems only to be active if you have a cylinder with a sensor on it. I have a combi boiler so its not active on my evohome controller.

Thanks though

 

[Bilabong007]

when you look at vokeras OT controller it can set the DHW temp. just why? i can only presume that because it doesnt get a signal it defaults to very safe and cold with honeywells OT system.

ways i can see round this so far:

Get a vokera OT controller and set the DHW then switch it over (hopefully it will stick on the setting)
Find a way to confuse the DHW sensor to heat the water more than 38 (ideally to 51 which i had it set to before).
Live with no OT control from evohome

 

[vulcancontinental]

We'll work it out.

The OpenTherm specification stipulates the control must be master of the boiler so we designed that way and disabled the HW selection on the boiler when it discovers an OT control. We told HW of this when we discovered their controller

The OT association now state they allow HW adjustment from the boiler.

Probably the easiest way is to use a OT control to set the DHW temp and switch it back afterwards to EH. I've only done this once and it worked but no guarantee. Are you willing to try this?

 

[Bilabong007]

Probably the easiest way is to use a OT control to set the DHW temp and switch it back afterwards to EH. I've only done this once and it worked but no guarantee. Are you willing to try this?

Im willing to give it a go yeah.

In my tests it resets after a reboot of the boiler so i will need to get a cheapo vokera OT and give it a bash. They don't seem to appear much on ebay, but i will have a wee look again today and see what i can find.

Hope you have a good day today and thanks

Graeme

ETA: I had a chat with a lovely guy at Vokera who suggested fitting a relay on one OT wire that breaks it when the DHW pressure switch is active. Unfortunately the boiler takes 5 mins to revert back to the internal settings after disconnecting the OT., not immediately after loosing the signal on my boiler

 

[Bilabong007]

With the help of a friend, I managed to obtain a vokera OT control, set the DHW temp then hot swap it for the Honeywell OT.
The boiler has retained the DHW setting and functions with the Evohome now. Im happy i managed to get it all to work in the end and Mrs B is happy, not freezing .

Shame such an expensive system like Evohome didnt red flag this or take provision in its software to control Vokera boilers correctly.

 

[Bilabong007]

Update:

Vokeras OT control allows the setting of the CH max T and climatic curve (also DHW T) and Evohome doesn't afaik. This means my boiler gets face meltingly hot and exits condensing mode on ramp up in the morning. I really don't see why it gets to 80... yes 80°C. Its quite frankly dangerous and a total waste of energy while posing a serious risk to my kids.

If these parameters are set by vokeras control - it only remembers the DHW temp when the honeywell is patched in.

Today im going to hard set my CH max T to 45°C using a jumper (JP7 closed) on the board. I designed/sized the rads for a slightly higher delta (30), but have since heavily insulated the house so im going to give it a try. I can live with a longer, but more efficient ramp up i think, but im going to test it.

In discussions with the manufacturer, i said "this could all be sorted by an arduino if i was a clever man and could code better". Then i found this https://tasmota.github.io/docs/OpenTherm/ - im not that clever, but others are

Anyone build their own OT interface? I think i could patch it in with honeywells, having zoning etc but set its parameters on the fly and even log the results on my server.

Resources so far:
https://www.bbc.co.uk/news/business-62900202 (the story that started it)

OpenTherm - Tasmota

Documentation (Wiki) for Tasmota

tasmota.github.io

OpenTherm Adapter

DIY OpenTherm Arduino/ESP8266 Thermostat Adapter

ihormelnyk.com

I ordered one of these > https://www.tindie.com/products/jiripraus/opentherm-gateway-arduino-shield/

 

[vulcancontinental]

Something doesn't sound right, Honeywell evohome is I think very capable, more capable than you've discovered so far. I'll tag someone who is very knowledgeable about evohome and perhaps they'll come into the plumbing forum. @Mike_W

 

[Bilabong007]

Honeywell evohome is I think very capable, more capable than you've discovered so far.

Unless it has a hidden menu i believed the same illusion.

 

[Bilabong007]

I finally managed to get Evo-home and my boiler to work together. Using the gateway arduino shield i can manipulate the OT commands, but let most of them pass through.

It required quite a bit of faffing, 2 types of "arduino" and a bit of c++ coding, but i got there in the end.

If anyone has similar boiler/stat compatibility problems i would be happy to help, or share the code etc if anyone has particular interest.

Big thanks to everyone who helped - esp @vulcancontinental