Honeywell Evohome with R8810 OpenTherm Gateway

[emmeesse68]

Hi there... I had to work a bit to find out an R8810 OpenTherm Gateway for my EvoHome system, I live in Italy and we are A LOT behind with this stuff.

Now I had an early implementation of my "DIY" EvoHome system, with two motorised zone valves for my old-style two zones (planning to switch to HR92s as soon as I can afford 11 of them ;-) ). Two BDR91 are driving those valves, that have an embedded switch that I used to control my (combined Ferroli BlueHelix Pro 32) boiler. So far, so good. Just a little puzzled about the continuous cycling of the zones/boiler when the actual temperature approaches the setpoint, but used to work quite reliably.

Now, since my boiler supports OpenTherm, I bought the Honeywell R8810 and set it up to control my boiler (just disconnected the wires from the valves switches and connected the R8810). First, the R8810 itself wasn't easy to pair to my Evohome controller. I tried several times, usually I get them paired after 8/10 tries...

Once the R8810 is paired... the behaviour gets odd. Sometimes it calls heat with both the zone valves shut off (that sets the boiler on, while water can't flow). Sometimes the other way round happens: zone valves open, boiler not firing.

Some other times, it seemed as the R8810 lost control capabilities to the boiler. Once it actually lost communications (I received a notification by email).

It's pretty weird that performing an RF test, the R8810 LED flashes red 5 times (that should mean excellent reception), but, differently from BDR91, the EvoHome display doesn't show any feedback.

Does anyone have any experience with an R8810? Is it always a nightmare, or maybe I have a faulty unit?


Thanks!

M

[The EVOHOME Shop]

Hi M,

Sadly this is something I can't help you with as we don't have the R8810 in the UK for evohome yet.

I understand the principle of OpenTherm but there seems to be some reluctance to its use, for what reasons I do not know.

Good luck in finding your answer.

Richard

[Woody]

Hi,

My experience is roughly the same. Binding the 8810 is not straightforward. The best way is to first 'clear' the 8810 by pressing the button for 15 seconds, after which the red led flashes quickly. Then remove and reconnect the 8810 cabling to the boiler for a couple of seconds. Then press the button on the 8810 for 5 seconds, after which the red led flashes slowly. Then bind the EVohome controller (via the system configuration menu) to the 8810. This seems to work most of the time for me. When finally bound I don't have problems with it; the led flashes green every 10 seconds and (so far) I never got any messages about comms loss.

I did have a problem once with the RF side of things, with a couple of HR80 valves in a distribution point. I mounted an RF-equipped alarm base station next to it (50 cm) and this caused all HR80's to open completely and never close again, heating up the living room to tropical temperatures. So you should take care of mounting other 868MHz equipment in the vicinity of Evohome equipment. Unfortunately more and more 868MHz stuff appears in the form of doorbells, remote power switches etc.

As for the working of the 8810, as I understand it by using OpenTherm the Evohome controller dictates how much heat (power) is needed in a given situation. This also sets the target temperature of the CH water. Modern, condensing boilers (only those have an OpenTherm interface) are most efficient when water temperature is below the dewpoint. Most likely the Evohome controller takes this fact into account when it detects a temperature curve in a zone coming down and decides that a little bit of heating now to maintain the selected temperature is better than a lot of heating later when the temperature drops under the set zone temperature. One (the only) of my big gripes with the Evohome system is that there is no way to make this visible. In my case this often leads to situations that I (on a laptop screen connected to my boiler) am able to see that heat is required and what water temperature is requested, but all zones (on the Evohome controller) are on their selected temperatures. Add that to the fact that the Evohome controller uses start - stop optimization and that the boiler itself is smart (the pump runs longer than the boiler is firing to use all of the leftover heat, the boiler is protected against cycling too often and against too little a difference between feed- and return temperature) and you end up with a system that mostly works great and does not use a lot of gas, but how it exactly does that, you have no way of knowing.

As stated elsewhere, IMO the Evohome controller would greatly improve if it had a diagnostics screen on which one could see how much heat is requested, which zone(s) request this, and which valves are open for how much. And a three-piece flame icon in every zone display on the controller screen to show low-medium-high heat, just as some other Honeywell thermostats have on their display. I am aware that this is largely to satisfy my curiosity, because one could argue that if the system does a good job, why would I want to look at diagnostics screens? But that is what you get from toying with stuff since my Meccano days

Paul

[emmeesse68]

Not having experienced comm losses anymore, I assume (better: I hope) communication problems are solved. Didn't do anything special, just rebound the R8810 one more time.

Meanwhile, I managed do get an OTGW in between my Ferroli BlueHelix Pro 32c boiler and my R8810. And I'm observing things that are happening because the EvoHome system is telling my boiler to, and not, as I was previously assuming, due to comm faults.

Briefly, there are times where the R8810 calls for heat and at the same time the Evohome shuts both my BDR91-driven zone valves. Thus the water temperature in the boiler raises quickly and the boiler itself stops the flame to protect from overheating. In a few minutes one (or both) BDR91 opens and water can start flowing again, bringing normality in water temperature. Then the Evohome stops the flame thru the R8810, by lowering control setpoint to 10 degrees for a few seconds (say 30?).

It appears as the Evohome is pulling pranks on itself... I'm just afraid of the stress this continuous overheating - protection can cause to my brand-new boiler.

I also ordered a 4 HR92 pack, so I can configure one of my heat zones with a multiple zone HR92-controlled (I plan to lock the valve in manually open position and remove the power wires from the BDR91, leaving it in place to rollback just in case something goes wrong). I'm suspecting that the Evohome has been optimised to be used with TRVs more than zone valves...

Too bad none of these diagnostic infos were available from the Evohome itself, as everybody seem to be pointing out this appears to be a major limitation - unless Honeywell is saving this opportunity for official support technicians, that *might* charge more than a few €€ for that

M

[emmeesse68]

Not having experienced comm losses anymore, I assume (better: I hope) communication problems are solved. Didn't do anything special, just rebound the R8810 one more time.

M

Since I wrote my last post, communication issues came back and I received an alert email as well.

Meanwhile my local reseller ran out of TRVs, so I'm stuck...