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I purchased this thermostat to use with my Ideal Logic 24 boiler.

However, it appears that it won't work because the thermostat requires power from OpenTherm and the older model of the boiler which I have uses the KM7 PCB which doesn't supply this power. It works fine with an older OpenTherm thermostat which is mains powered.

I wondered if I inserted an Opentherm Gateway whether it would solve the problem by providing power to the thermostat?

I can not find much information about this thermostat on the internet. If it requires Opentherm 3.0 compliant smart power, then the OTGW can provide that. If it uses some proprietary modification of the interface to supply even more power, then you're out of luck.

Thank you for your reply.

On the back of the thermostat it says 18V 17mA

When the thermostat is connected to the boiler a multimeter across the OT wires reads about 5VDC. Without the thermostat it reads 28VDC.

I am told that when the thermostat is connected to the newer boiler it reads about 12VDC which suggests it's supplying more power.

So it sounds like your gateway might solve the issue.

Is your gateway kit still available somewhere or is it necessary to buy the Nodo kit?

Best wishes

Tim

That sounds like it wants the High Power mode introduced by the Smart Power feature. The OTGW is able to provide that, while still only using standard (Low Power) mode on the boiler interface.

If you don't want the kit offered by the Nodo shop for some reason, you can buy the circuit board and components from other sources. All options I know about are listed on the site. Make sure you have a way to get the PIC programmed the first time.

Presumably it wouldn't work as a repeater without the PIC?

Correct. The PIC isn't purely decorative.

I guess there is some active negotiation involved in boosting the power

I was wondering if it's worthwhile building a minimal gateway that just increases the power but does nothing else. Looks like it's more sensible to use a standard gateway.

Thanks

That wouldn't work. The thermostat has to start in Low Power mode. It then sends a Master Configuration message (Msg ID 2), indicating it wants to use Smart Power. Only when the slave doesn't object to that message, the master is allowed to switch power modes. When Smart Power is acknowledged by the slave, the master may switch between Low Power, Medium Power, and High Power at any time. It doesn't have to choose one mode and stick to it. For example, the iSense will normally run on Low Power and only switches to Medium Power when the backlight is on.

Does the OpenTherm gateway answer the request or does it just pass it through to the slave (boiler)?

In my case the problem is that the boiler won't supply more than low power so presumably it will ignore the request.

The gateway handles the request, as you can see in the following log excerpt:
Here, the thermostat sends a message indicating it employs Smart Power (ID2:HB0). The boiler responds that it doesn't support that (Unknown DataId), but the OTGW turns that into a Write-Ack to the thermostat. Next the thermostat verifies that Smart power is actually working by switching to High power mode and exchanging a status message. Then it changes back to Low power mode. These power mode changes only happen on the thermostat interface.

I hope it's clear that this will only work in gateway mode. In monitor mode every line change is transparently passed on by the OTGW. So in that case it can't modify the response to Msg ID 2. Any Smart power mode change request would also be forwarded.

That's helpful, thank you.

Which boiler and thermostat were in use when that log was made?

The log was made with a Remeha Avanta boiler and a Remeha iSense thermostat.

I have ordered a gateway from the Nodo shop and will report back when I've tried it out.

I have now obtained an OTGW from the Nodo Shop and connected it to my Ideal Halo Lite thermostat.

When the thermostat is connected the gateway reports:

17:39:54.427663 High power
17:40:06.479674 Low power
17:40:06.637661 T90020100 Write-Data Master configuration: 00000001 0

The final message repeats at about 1.25 second intervals

Nothing appears on the thermostat display.

That's weird. The gateway should not accept Smart Power until it has received MsgID 2 with HB0 set. Also, you must connect the gateway to a boiler. It can work without a thermostat, but not without a boiler.