Evohome + Opentherm v Evohome + Boiler Outside Weather Compensation

[bruce_miranda]

Also lets be clear. The VR33 is simply an Opentherm to eBUS bridge. Its a part made by Vaillant, not in someone's garage.

[The EVOHOME Shop]

I didn't leave the boiler in this bridged configuration for long. Maybe I should have done. What I did see was the boiler was on even when there was no call for heat and stayed on. It fired until the max temperature was reached and then just cycled. You could see the icons on the boiler saying there was a call for heat.

Also to be perfectly honest, I prefer my Hybrid system. Because that way I am sure that the boiler is being fired by a zone valve only after it opens. I didn't like the fact that zone valves and boiler firing were going to be controlled independently in an ideal set-up (am old school and not at least when RF communications is involved). I did notice that the Opentherm bridge was quicker to react to a change that the BDR91s getting their command to open.
I now have a system that could always act as a non Evohome system, should it need to. I just need to put the time clock back and turned off.

Can we bring this back up again to try and get a solution? I would prefer a non hybrid solution, but as I have just read in a Keston Qudos manual it looked like the Keston required a switched live demand before it would modulate with OpenTherm (OpenTherm slave thermostat situation).

[bruce_miranda]

My boiler is a Vaillant ecoTec plus 438. My boiler seems to need a switched live to fire up.

I don't have dedicated terminals for a 24V RT and Burner Off. I just have two eBUS connectiions, 7-8-9 connections which are for the old 24V analogue thermostats that were never used in the UK. Vaillant tell me that for the boiler to understand any eBUS command I need to use the Vaillant wiring centre. I don't think that advice is entirely accurate because my Opentherm bridge is able to alter the target flow temperatures, just can't fire the boiler up as top brake and Stuart have been able to.

If I bridge 3 and 4 my boiler fires up even if I don't want it to. If I leave 3 and 4 unbridged then the boiler never fires up. So currently I use the terminal 4 to fire the boiler via the zone switches.

[bruce_miranda]

Another member who has a similar boiler wiring seems to have gotten his OT bridge to fire the boiler by adding a jumper between 7 and 9. 7 8 9 are the connections for an analogue boiler demand control. 7 is the signal, 8 is the +15V and 9 is GND. Depending on what the voltage is set at 7, the boiler is able to vary the demand. In the UK the manual clearly states NOT to use those terminals. But by putting a jumper between 7 and 9, that is effectively saying Burner Off. Which is what the VR33 manual asks you to do. So maybe that is what I was missing.

Could anyone on here please confirm what value they are seeing on D.16 on the boiler. Is it always 0?

[bruce_miranda]

I have finally managed to get the Opentherm bridge to fire up my boiler on a Vaillant ecotec plus 438. I put back the jumper between 3 and 4, without this the boiler doesnt fire up. Once 3 and 4 is connected the boiler is expecting to see an analogue controller on terminals 7 8 9, otherwise it is constantly firing up. If i put a jumper between 7 and 9, the D.09 just shows me 0, which basically means that the OT bridge isn't doing anything. If instead I put a jumper between 7 and 8, the OT bridge is not only able to vary the target temperature but is also able to fire up the boiler! So it looks like a jumper between 7 and 8 is the equivalent of the 24V RT on the modern boilers.

[Ro-]

Do you know if it is possible to use the VR33 to connect Evohome with OpenTherm bridge to a Glow Worm boiler (Energy 30s)?

Many thanks,

[bruce_miranda]

The VR33 is a Vaillant part for Vaillant boilers in NL. UK doesn't even sell or support this part. So a lot of us have taken the risk of trying it out on various Vaillant boilers. Trying it on a Glow worm may be a step too far. You need to look for a Glow worm equivalent Opentherm interface, if your boiler doesn't already support it.

[HenGus]

There really isn't much enthusiasm for Opentherm within the installer community. I have now been in contact with 3 ecotechnicians and only one is genuinely interested in doing the research and quoting for an ATag boiler with Opentherm. A N Other told me that he has installed Evohome in many properties but can see no benefit (financial) in going the Opentherm route. He admits that he prefers to install Valliant or WB boilers although he is trained on Viessmann and Intergas. A third has strongly advised that I shouldn't consider Intergas/Opentherm with Evohome until ongoing data issues have been resolved: the safer route would be Intergas Eco with WC plus Evohome standard control.

The irony here is that many manufacturers are now pushing their Opentherm controls (Nest, Danfoss and Honeywell for example). Is this just a case of installers wanting the safe and proven route where they know that they can rely on full boiler manufacturer support if they fit the recommended controls ?

[DBMandrake]

A couple of comments on the feedback from installers from an outsider.

One is why does benefit always have to come back to financial savings ? If OpenTherm gives smoother, better control of temperatures in the house that improves comfort, but doesn't save any additional gas over and above any savings already gained from TPI, (and I'm not convinced this is actually the case with a modulating, condensing boiler, which should theoretically run more efficiently with its flow control directly modulated instead of being switched on and off repeatedly every 10 minutes) is that a reason not to bother with it ?

If it was only about ROI then all the current smart heating controls (including evohome) would be a big fat fail because they're too expensive to pay for themselves in any reasonable amount of time from gas savings alone. When they did eventually pay for themselves they would by that time be obsolete.

Comfort and flexibility of control has to be a major deciding factor in buying the current set of smart heating controls. Everyone is looking for a magic bullet to save on their gas bills but do current smart heating controls in reality give anything more than an incremental improvement here ?

The other thing is, you're dealing with an industry that is still perfectly happy to install brand new systems in 2016 that consist of a simple on/off timer no smarter than a VCR timer, (remember those) single hall stat for an entire house and mechanical (expanding wax pellet) TRV's "calibrated" in 1 to 5 for individual rooms. This hasn't been state of the art for a couple of decades now and I think people on this forum realise just how crude this technology really is or they wouldn't be here. Expecting installers to race in and embrace new, more complicated technology that makes their job more complicated is a bit of a hard sell.

Installers are happy to "stick with what they know" - simple systems that are for the most part simple and easy to understand and troubleshoot, but hardly state of the art. There is no incentive for them to train themselves on smart home controls that just make their job more complicated and have more likely hood of return visits for faults or the potential for difficult to diagnose faults. Nobody can deny that the current smart home controls are more complicated and have more things that can go wrong than a conventional system.

So I would put it down to a certain degree of apathy and a willingness to just do things the way they've been done because that's what they're familiar with and what they feel comfortable in dealing with. Failure to embrace new technologies and systems through inertia, apathy and ignorance is a major problems in many fields these days. Eventually those people will age out of the system and new people will come along that are comfortable with newer technology and paradigms, but it takes time.

[paulockenden]

You know in another thread I mentioned my missus struggles to understand Evohome? Well the clowns who installed my system weren't that far behind.

Double bound BDR91s, mounted next to each other, one of my downstairs rads bound to an upstairs bedroom, etc. etc.

I'm sure there are lots of good installers out there, though. Perhaps some even lurking here and reading this? You'd like to think so, wouldn't you?

P.