OpenTherm control behaviour

[dty]

That's my feeling too, although it's almost certain that boilers that do allow you to set a maximum flow temperature currently implement the limit simply using clipping... but if we're going to build an intermediate interface we can do better than that.

That would imply that Evohome is happy to work on that basis, however, and would remove an assumption (i.e. the possible requested temperature range)

[StephenC]

I have a spare (i.e. I have 2) R8810 Opentherm bridge if anyone can, or wants to assist here that doesn't already have an OT bridge.

It doesn't have a back panel (i.e. I only have 1), but that is just for wall mounting and connecting power/data wires anyway. The pcb and circuit board for the R8810 is all contained on the front panel.

IMG_3434.jpg

[blowlamp]

Hi, new member here.

When I installed my system last year I hadn't heard of any of the Evohome stuff so a Remeha iSense controller was fitted and so far, it's working very well.

Here's a link to the Installer Manual which shows the various control strategies available to tweak its performance.

My system details: Intergas HRE 36/30 (Modulating Pump) with weather compensation, Remeha iSense (Wireless) OpenTherm control unit and Pegler I-Temp TRVs.

The above is installed in a typical mid 1950s, 3 bed detached, bay-fronted house with double glazing and reasonable insulation.

I find that weather compensation & OpenTherm cooperate quite nicely and after some experimentation with the available strategies, plus some adjustment of the heating curve, I've got a good setting for my house. I oversized all the radiators to achieve low flow temperatures and consequently find the boiler to be in a semi-permanent state of condensing. I don't recall seeing a flow temperature reach 60 degrees, but I may have missed one that did, however, return temperatures are always cool enough to allow the pipe at the boiler to be held indefinitely without discomfort - not scientific I know, but the difference between flow & return temperatures is remarkable.


Martin

[kimber.kimber]

Chased up Ideal today, and they are discussing this with the R&D department. I'll update when they come back with something. Looks like they may not have had many people come back with queries on it so far.

[HenGus]

Just to add an update to this thread on Opentherm behaviour. I really should have taken more notice of the installer instructions that came with my new boiler. Earlier this week, I found out that I can reduce the boiler flow temperature below the maximum TSet temperature in the boiler profile. We had the heating on the other evening, and I set the max flow temp at 60C to maximise condensing. There was no HW demand. The following morning, I noticed that the boiler was cycling in an ON HW period but with the boiler close to its set temperature - but not actually at it. (Boiler set at 60C and HW target temperature 62C).

As reported in another forum, I assumed that this was a rogue heating demand even though heating was at permanent OFF; all zones were at 5C and all the radiators were cool. Having now raised the boiler flow temp back to 70C everything is now fine. My little 'experiment' would seem that to indicate that it is the boiler max temperature that limits the Evohome HW max: not the profile TSet temperature as I first thought.

Conclusion: issues as reported above would seem to suggest, to me at least, that Evohome/Opentherm compatibility issues are more down to the boiler manufacturer than Honeywell. I am sure that this debate will continue. For my part, I have learned a valuable lesson: the boiler flow temperature should not be set lower that the HW set temperature.

[fergie]

No doubt I will be shot down in flames, but there is no doubting in my mind that all the reported OT issues are down to some manufacturers using their own modified / cut down versions of OpenTherm.

Its a pity as it defeats the ethos of OT and also causes chaos for consumers.

[bruce_miranda]

No shots from me, I agree...

[blowlamp]

No doubt I will be shot down in flames, but there is no doubting in my mind that all the reported OT issues are down to some manufacturers using their own modified / cut down versions of OpenTherm.

Its a pity as it defeats the ethos of OT and also causes chaos for consumers.

The rather basic understanding I have of TPI thermostats is that they are intelligent 1 way boiler switches that have the capability to achieve a set temperature through varying the flame on/off ratio over a defined time period and I believe Evohome, at its core, is such a TPI device.

On the other hand, OpenTherm is designed as a 2 way modulating system that not only sends instructions to the boiler, but also receives them and acts upon them.

From my perspective as a non Evohome user, I can't help but think that Honeywell's integration of OpenTherm with this particular product is the fundamental problem as it doesn’t seem to have a full implementation of the necessary features to allow it to properly control the boiler.

The Remeha iSense thermostat/control I have, controls an Intergas boiler with no issues at all. In effect, the iSense has remote control of the boiler and overrides certain settings such as the weather compensation curve (replacing it with its own user-defined one), max flow temperature and DHW temperature, etc. It also relays other information, like system pressure, fault conditions and outside temperature via the boiler’s weather sensor.

I’d (almost!) bet good money that an iSense controller (which is OpenTherm V3.0 certified) would work reliably with any of the problem boilers mentioned here such as Ideal, Veissmann or any other make which claims OpenTherm compatibility.

Martin.

[fergie]

Interesting. Can the isense control multiple zones etc?

[blowlamp]

Interesting. Can the isense control multiple zones etc?

Apparently it can do 2 zones with some add-on called c-Mix, but I don't know what that is.
So it's not comparable to Evohome in that way, however, I find the iSense control quite suitable for the size of our house & our various needs.

Despite being pretty audible in a quiet room, I found the recently added I-Temp TRVs to markedly improve comfort and control of individual room temperatures, which gives us a kind of 'poor mans' Evohome system albeit without the ultimate control afforded by Evohome.

Just for information: Our house is currently at 20°C whilst it’s dropped to 12°C outside. I’ve upped the controller temperature setpoint to 22°C & the boiler has fired up from being virtually cold. The iSense is reporting a heating water flow setpoint of 44°C.


Martin.

[kimber.kimber]

Just to add a quick update, I chased up Ideal on this today. They replied saying they are in talks with Honeywell but this obviously take some time to get a solution.

It's Ok, there's about 5 months before I need the heating again!

[Rameses]

Sounds like we have same problem.

@ Rameses - is this something that Honeywell can look at now we are seeing multiple boiler vendors expecting the OT controller to set the max ch flow temp?

I note the new Nest v3 seems to have the ability when connected via Opentherm. So appears it is possible from a protocol perspective.

I have passed on to the team. And Opentherm are in the mix as well.

[fergie]

Would also be great if Evohome could be developed to display both the information being sent and also display / utilise the boiler info being fed back.

[kimber.kimber]

Gave Ideal a nudge on this the other day, and got the following back...

Hi Ian,

Just a quick update, Honeywell have provided us with updated boards to resolve your issue.

We are currently doing our own testing on these and expect them to be ready for use in around a month.

As soon as I hear these are updated I will organise yours to be replaced.

I hope this helps

regards

Richard Maskell
Domestic Technical Team Manager


Once I hear back from them, I'll do a little more digging into to find out what's changed. Not going to become a PITA if they are going to update my boiler...

[HenGus]

Gave Ideal a nudge on this the other day, and got the following back...

Hi Ian,

Just a quick update, Honeywell have provided us with updated boards to resolve your issue.

We are currently doing our own testing on these and expect them to be ready for use in around a month.

As soon as I hear these are updated I will organise yours to be replaced.

I hope this helps

regards

Richard Maskell
Domestic Technical Team Manager


Once I hear back from them, I'll do a little more digging into to find out what's changed. Not going to become a PITA if they are going to update my boiler...

I am a bit confused. The way that this reads is the Ideal buys its boiler PCBs from Honeywell. It seems strange to me that if one supplier is manufacturing both the opentherm bridge and the PCB that this type of issue has arisen.