R8810a opentherm bridge with ideal logic +

[Speedychuck]

I took delivery of my evohome system yesterday from evohome shop. Overall I am happy, but at the moment I am having to use the relay box instead of the opentherm bridge.

The bridge doesn't appear to be powering up. Apparently the LED should flash every second once powered but it doesn't. It also continuously calls the boiler to heat.

I connected the opentherm bridge to the opentherm connections on the boiler (I have made the connection inside too) but the opentherm bridge doesn't seem to power up. Has anybody else used it with a logic plus? Opentherm was my main reason for choosing evohome as I want the modulating control.

[top brake]

Please check with Ideal that that model has OpenTherm enabled. You usually need a patch cable to enable.

[top brake]

Also check how how the heat demand has been configured in installer mode SYSTEM DEVICES

[Speedychuck]

Thanks for the advice.

The model is an ideal logic+ 35. It has opentherm and comes complete with the cabling. It just has to be connected internally. Lesser models don't come with the loom, but it comes as part of the weather compensation kit, which I also have. (Spare loom).

I never tried to configure anything as the r8810 doesn't power up. I'll have another go now and see if I can make any further progress. Perhaps the LED doesn't work in the 8810.

[top brake]

Please check it is assigned correctly as I suggested

Thanks for the advice.

The model is an ideal logic+ 35. It has opentherm and comes complete with the cabling. It just has to be connected internally. Lesser models don't come with the loom, but it comes as part of the weather compensation kit, which I also have. (Spare loom).

I never tried to configure anything as the r8810 doesn't power up. I'll have another go now and see if I can make any further progress. Perhaps the LED doesn't work in the 8810.

[Speedychuck]

I've done as you said, problem is, I can't bind the opentherm bridge, without it being powered.

I've checked and double checked all the connections, but I can't get the bridge to power up. Do you have any experience with connecting the r8810 to an ideal logic +?

[top brake]

Please contact Ideal for advice as it sounds like a connectivity issue with the OpenTherm terminals.

I've done as you said, problem is, I can't bind the opentherm bridge, without it being powered.

I've checked and double checked all the connections, but I can't get the bridge to power up. Do you have any experience with connecting the r8810 to an ideal logic +?

[Speedychuck]

What voltage should be on the opentherm terminals? Ie- what is required to power the r8810?

[top brake]

What voltage should be on the opentherm terminals? Ie- what is required to power the r8810?

It's a loop powered low power digital interface

[Speedychuck]

I've found some of the info I was looking for by trawling the opentherm standard

3.3.2.1 Room Unit Current
Guaranteed current available from the line is the minimum allowable idle signalling current (5 mA). This includes the current necessary to operate the regulator which develops the supply voltage in the room unit.
Room unit current consumption : 5 mA max.
3.3.2.2 Room Unit Voltage
The minimum voltage available to supply the room unit circuitry is a function of the implementation of the room unit communications interface. It is directly related to the Idle Line voltage and to the voltage drops associated with the polarity management circuitry and the voltage signalling circuit in idle state.
As a guide, a nominal voltage of 3.3V is achievable with a low cost implementation of the interface.

So I'll be checking this later on when I get back. Interestingly, opentherm will call the boiler if there is a dead short on the cables. So that it can operate like a normal boiler using the same control. This appears to be what is happening, so I'm wondering if perhaps I have a fault in the opentherm bridge.

The boiler unit must support an important installation feature which allows the terminals at the boiler to be short-circuited to simulate a heat demand such as can be done with existing on/off boilers. The boiler unit should interpret the short-circuit as a heat demand within15 secs of the short-circuit being applied. This must be supported by both OT/+ and OT/- boilers.

[paulockenden]

Do you have a DMM (multimeter)? If so, check that the boiler is actually providing the voltage needed for the bridge.

[Speedychuck]

Having read further, I'm beginning to wonder if this is an issue with the type of opentherm supported by the boiler. It appears there are two "versions" of opentherm: ot+ and ot-. Devices can be one, the other or both. I know the R8810 is at least ot+, and I'm thinking the boiler must be ot-.

Does anybody know if the r8810 is ot+ and ot- compatible?

The boiler appears to be working correctly. I'm going to speak to evohome shop and ask to try another r8810 in case this has a fault, but if not, I think I'm onto a loser here.

[paulockenden]

I didn't think ot- was used much in the real world?

Seriously, if your device is isn't powering up the first thing I'd check is that there's actually power available.

P.

[top brake]

No the boiler is fully compatible with standard OpenTherm. Please follow my advise and contact Ideal to check that that model OpenTherm is enabled.

Having read further, I'm beginning to wonder if this is an issue with the type of opentherm supported by the boiler. It appears there are two "versions" of opentherm: ot+ and ot-. Devices can be one, the other or both. I know the R8810 is at least ot+, and I'm thinking the boiler must be ot-.

Does anybody know if the r8810 is ot+ and ot- compatible?

The boiler appears to be working correctly. I'm going to speak to evohome shop and ask to try another r8810 in case this has a fault, but if not, I think I'm onto a loser here.

[Speedychuck]

I'm gonna rob a multimeter from a friend later. Mines in my toolbag somewhere in the North Sea at the monent. I'm an electrical/electronics tech by trade and I don't have a multimeter in my house! Brilliant.

The reason I say about ot- is that according to the standard, only products which are ot+ can carry the opentherm logo, and I can't see the opentherm logo on any of the documentation related to the boiler, despite the fact that it is clearly marketed as opentherm compatible. As said, it's an Ideal Logic+ 35 Combi, I've googled and checked the spec on the boiler and it doesn't mention whether it's ot+ or ot- so if you or anybody else knows, it might answer my question.