viessman/opentherm/evohome/pandora poor DHW

[sandyman44]

That isnnae a Y plan.

I know its not a y-plan as strictly defined based on where and what type of valves, how they are controlled, etc. But it gives a logical OR, i.e CH OR DHW, which is exactly what Y-plan does, therefore to me, that proposal was pretty much analogous to running the system as Y-plan.

That really isn't a Y plan

ok, W plan then.

 

[simond]

thanks. as part of this test, do I also need to send a live to the relevant terminal on the cylinder demand terminal box? am I correct to assume that is there to tell the modulation logic to stay out of the way, and thus makes the difference between the boiler running in CH-mode, cool and efficient, and DHW mode, hot and full-power? I haven't had the lid off yet, will do so , however I very much expect this terminal box is not connected

Right, you turn off the power, disconnect the Viessmann interface box from the boiler. You link the Switched L to the Permanent L in the right hand part of the boiler control box.

You then select HEATING OFF on Evohome, pin the motorised valve over to hot water, and reinstate the boiler power.

The boiler will then treat the demand as normal with no OT involvement. Assuming (as I do, because we've fitted lots of WB1Bs) this works and you get 75C, throw away the Viessmann interface box and the Evo OT relay, and use on/off BDR91s with your Evohome instead.

I'm intrigued whose idea it was to create a system with this particular mix of hardware. Was it you or the installer?

 

[sandyman44]

thanks. as part of this test, do I also need to send a live to the relevant terminal on the cylinder demand terminal box? am I correct to assume that is there to tell the modulation logic to stay out of the way, and thus makes the difference between the boiler running in CH-mode, cool and efficient, and DHW mode, hot and full-power? I haven't had the lid off yet, will do so , however I very much expect this terminal box is not connected

Right, you turn off the power, disconnect the Viessmann interface box from the boiler. You link the Switched L to the Permanent L in the right hand part of the boiler control box.

You then select HEATING OFF on Evohome, pin the motorised valve over to hot water, and reinstate the boiler power.

The boiler will then treat the demand as normal with no OT involvement. Assuming (as I do, because we've fitted lots of WB1Bs) this works and you get 75C, throw away the Viessmann interface box and the Evo OT relay, and use on/off BDR91s with your Evohome instead.

I'm intrigued whose idea it was to create a system with this particular mix of hardware. Was it you or the installer?

ok, makes sense. so we are just giving it voltage on the room stat call for heat terminal. I will try to see if I can test this weekend. clearly you know the WB1B and expect this to work. do you expect it to go straight to 75, or work its way slowly up? if want it to go straight there, do we also need to send voltage to the DHW terminal (I presume this is the hot water doofer that dan has been referring to)? Some documentation I've found

Wb1b

• sandyman44
• 14 Apr 2016

wb1b control inputs and temps

suggests that voltage on that terminal makes the output fixed at 78 (which is exactly what we want).

regarding the system specs, I told the installer I wanted evohome , and a good quality (not a cheap) new boiler. They recommended the viessman. regarding OT, I had read one or two things about opentherm on forums and asked them if using it would make the operation more efficient by enabling the boiler to down modulate (bear in mind I was coming from a 1999 or 2000 potterton kingfisher that knew nothing of modulation, so getting the power level down when not needed seemed like the sensible thing to want) . They said it would and it was all compatible, happy to recommend it, knew how it worked, etc. The exact list of evohome/boiler/OT parts and what is connected where and how is all down to the installer. I didn't tell them I wanted my HW heatbank to still work properly afterwards, but that should have been obvious! I know how most of it works, and I could potentially have specced it myself and just got a gas fitter to do the boiler level bits.. but I didn't have the time, and I wanted a turnkey supported solution with the design owned by the installer not me. Hence, if anything needs changing , I am insisting the installer does it at no cost to me. I think whilst we are still in the realm of small capital cost stuff (wiring changes, swapping controllers , OT for BDR's, etc) and their time they are not pushing back on that. I hope it doesn't get to anything with substantial capital cost.

 

[sandyman44]

thanks. as part of this test, do I also need to send a live to the relevant terminal on the cylinder demand terminal box? am I correct to assume that is there to tell the modulation logic to stay out of the way, and thus makes the difference between the boiler running in CH-mode, cool and efficient, and DHW mode, hot and full-power? I haven't had the lid off yet, will do so , however I very much expect this terminal box is not connected

Right, you turn off the power, disconnect the Viessmann interface box from the boiler. You link the Switched L to the Permanent L in the right hand part of the boiler control box.

You then select HEATING OFF on Evohome, pin the motorised valve over to hot water, and reinstate the boiler power.

The boiler will then treat the demand as normal with no OT involvement. Assuming (as I do, because we've fitted lots of WB1Bs) this works and you get 75C, throw away the Viessmann interface box and the Evo OT relay, and use on/off BDR91s with your Evohome instead.

I'm intrigued whose idea it was to create a system with this particular mix of hardware. Was it you or the installer?

well, the plot thickens. My installers specified opentherm, but having inspected everything in detail at the weekend, there is no opentherm!
Nothing is plugged into X21 in the boiler. I have been installed a straightforward BDR91 boiler relay, sending switched live to the roomstat call for heat terminal on the right hand side of the boiler. thats it. Leaving aside the obvious for the moment and moving back to the technical:

my system has been already running in the mode you suggested I test for 5 months. I have done numerous tests previously, exactly as you describe with the heating off and hw on - and we now know that the only signal the boiler was ever getting was "be on". The boiler does get to 75, but it takes forever to get there - it seems to be completely dependent on fairly hot (60ish) water coming back from the cylinder before it will get to that temp. And after not very long it shuts off (I guess because it thinks the return is too hot) and I end up waiting for ages for the 68degree water to finish off warming my cylinder.

I've found the red spade terminals on the wiring loom marked "5" inside the boiler unused, the docs say these are the ones for the dhw cylinder kit input, am I correct that if we send 230v into that kit, it sends the correct level into those terminals to persuade the boiler to run at high temp? Dan is this the hw doofer you kept referring to?

I also now believe the wb1b must be overmodulating, as there can never have been any OT input, whatever it was doing was entirely down to the boilers internal control plane. I could never understand why it did this: for example, this morning, I was up unusually early at 5.30, same time as the heating fires up in two rooms downstairs (kitchen and hall, total of 3 rads and a wet-plinth). It took almost an hour for the flow temps to approach 70. And the kitchen rads were cold for more than half an hour, most of this time the boiler was on power level 1 and flow 40. It seems to me the only thing it cares about is the delta between flow and return - so with a return of 20, its happy to send flow out at 40. how the heck do you persuade this thing to give it full blast in a hurry as the heating cycle starts for the day?

 

[Dan Robinson]

there is no opentherm!

Oh Dear. Where is the OT bridge you thought you had paid for?

Dan is this the hw doofer you kept referring to?

Yep.

how the heck do you persuade this thing to give it full blast in a hurry as the heating cycle starts for the day?

This is not really how the system is supposed to work, between optimisation and the OT (which you might one day get), the idea is to run the boler long, low and slow for heating.

Hence the need for the hot water hickory doo dah; and why I tend to run these set ups as hot water priority/W plan ... As Honeywell suggested after much interaction with the likes of us out there that fit this stuff.

 

[Agile]

What a lot of detail to plough through.

As far as I can see the system is not set up to give the higher flow temperature required for water ( store ) heating.

That has to be set up to be hot water priority so the boiler delivers an elevated temperature for reheating the water only. It needs a little control PCB from Viessmann.

When that is satisfied the boiler can revert to providing the heating under the control of the Evohome system with the hoped for OT control.

Amazing how some installers can get it so wrong.

Mystery Man will be tearing his hair out. ( But I think he did that ages ago ).

 

[sandyman44]

Oh Dear. Where is the OT bridge you thought you had paid for?

good question. I've written a "substantial" email to my installers, still waiting for their reply. Its not about the cost of the OT unit (bugger all in the grand scheme) its the 5 months of hassle trying to figure out why it wasn't working .... and all the time the assumptions on what was going on were unfounded.

Yep.

thanks. now I know what I need to get to fix the HW issue.

This is not really how the system is supposed to work, between optimisation and the OT (which you might one day get), the idea is to run the boler long, low and slow for heating.

would having OT after all perhaps indicate to the boiler that the CH load is a cold start and persuade it do run hot for starters? and then backoff to low?

Hence the need for the hot water hickory doo dah; and why I tend to run these set ups as hot water priority/W plan ... As Honeywell suggested after much interaction with the likes of us out there that fit this stuff.

yes it makes sense for it to be W plan now that I know the above. i.e. if you use the hot water override input to run the boiler at 78, you don't want that charging round the rads just fire it at where its needed , i.e. the cylinder, then go back down to cooler for condensing mode for the rads.

 

[Dan Robinson]

would having OT after all perhaps indicate to the boiler that the CH load is a cold start and persuade it do run hot for starters? and then backoff to low

OT is a weird thing. It is actually only a communication language/protocol. What the end result is for you depends on the interrelationship between the controller and the boiler.

On first reading the protocol it appears that the controller (Evohome) tells the boiler what to do and the boiler is just a slave.

In actual fact there is a symbiotic relationship and the level at which the devices talk to each other depends on the different aspects of the protocol they may or may not use.

I have Evohome on a W plan at home. At Christmas I took out my Coopra boiler that worked beautifully on the control system exactly as I had sized and predicted. Flow temperatures were low, and the boiler ran for a long time in the most efficient way it could.

At Christmas I was getting cabin fever so decided to swap the boiler for one of my beloved Intergas boilers. the end result was very different. The boiler still operates more or less 100% condensing for heating, btu the modulation range (temperature not kW) is much much smaller as it doesn't seem to want to cope with the extra zones.

Put a single zone OT controller on and it works much more like the Coopra.

Look at the two PCB's of the boilers and it might well be down to processing capacity - I know the Intergas PCB doesn't have a lot of bells and whistles.

However, getting the level of detail I want from either Honeywell or Intergas is an exercise in futility and the parts of the companies I want to talk to are not interested in dealing with installers and even less so with end users. So, even when you do get the system up and running as intended, the only people able to tell you if it is working correctly are going to be those that have it themselves, or are like me and willing to invest hundred if not thousands to do the testing the manufacturer's are not willing to publish their own results of.

 

[Dan Robinson]

We use OT incorrectly as a term on a daily basis... It doesn't guarantee the method of the system operation. As 3rd Gen nest owners discovered pretty quickly

 

[sandyman44]

would having OT after all perhaps indicate to the boiler that the CH load is a cold start and persuade it do run hot for starters? and then backoff to low

OT is a weird thing. It is actually only a communication language/protocol. What the end result is for you depends on the interrelationship between the controller and the boiler.

On first reading the protocol it appears that the controller (Evohome) tells the boiler what to do and the boiler is just a slave.

In actual fact there is a symbiotic relationship and the level at which the devices talk to each other depends on the different aspects of the protocol they may or may not use.

yeah, I had a good read of the protocol spec as well a couple of months back once I started seriously trying to understand what was going on for myself. I design large and complicated country-sized networks that run internet service providers etc for a living, so I have to know a lot of protocol specs for boxes talking complicated stuff to each other, albeit for different protocols of course. however without a debug tool to tell you what they are saying to each other (has anyone home-brewed one with a raspberry pi or similar?) its a bit moot, as you say, swap your boiler and test it if your in the trade and can do that.

 

[Dan Robinson]

https://www.kiwi-electronics.nl/opentherm-gateway-kit

It is on my list of things to make... but my list of things to make is a third of the way down my list of things to do which is fecking mahoosive.

You have two layers of communication though.... a bit like Bluetooth talking to a phone that is using WiFi to get its data.

OT is giving the boiler instructions, but you have Ramses going between Honeywell devices so Evo is working on two different levels and might not be as you expect. With OT it is working to the most demanding part of the system. In theory, with hot water it sends a 100% load command to hte boiler, but the boiler has its own logic that separates hot water and heating... It would be nice if the OT implementation told the boiler it was hot water (and that the boiler would listen too).

Evohome has some idiosyncrasies of its own too; the phrase "a watched pot never boils" goes to a whole new level



Will be interesting to see what their excuse is for giving you TPi instead of OT though?

 

[Dan Robinson]

P.S. If you make one of those - I'll buy a USB version off you

 

[Twenty Four]

P.S. If you make one of those - I'll buy a USB version off you

If you refer to your link then wouldn't this be the way to go? https://www.kiwi-electronics.nl/opentherm-gateway-usb-voorgesoldeerd

 

[Dan Robinson]

Nice

 

[Agile]

Gratis verzonden too!

How do you read what it will do in English?

I wonder if Dan can afford one?


Simple question, when told its heating hot water, does the IG run/accept/expect a lower diff?

Tony