I'm writing this because it was very difficult to find anything concrete about whether boilers were fully compatable with Drayton's implementation of OpenTherm.
There were many posts, with some replies from people who where guessing, that there were problems with Draytons implementation of OpenTherm. Other threads stopped abruptly when it appeared the author had solved the problem... without any details of what had happened.
I have been using the Wiser system with a Worcestor Bosch combi using relay control and it has been good. It may only be a one bedroom flat but its an old rambling building and I currently have 4 Wiser Radiator thermostats and two room thermostats. Finally the flat is a fairly consistent temperature.
I have had problems with the Drayton Wiser Hub. The system kept on being unavailable. This was finally solved using a £12 wifi extender from Argos. Even though the wifi signal was at about a half according to the diagnostics on the app, it obviously wasn't working properly. It didn't just not work, very weird things happened when trying to get it to work. After the wifi extender, which is sited quite near it, I have had no problems at all. Coverage to all the peripheral has been pretty good with one living room radiator thermostat dropping out occasionally. Then it reconnects again.
I was having the boiler moved and decided to replace the aging Worcester with a Baxi 624 combi which, a message board suggested, should work with Drayton's OpenTherm. There were reports that there were problems with domestic hot water (DHW) as the Baxi expects DHW temperature messages and the Wiser does not supply them. By the law of OpenTherm you do not need to send them, but the Baxi controllers do so it expects them.
The proliferation of 3rd party controllers for boilers has meant people like me tinkering with heating systems which they would never have been interested in before. It also means that people are asking Boiler Installers to install boilers with controllers where there is no proof they will be compatible. I have a deal with my installer that we will go back to relay closure if the opentherm proves problematic.
When using opentherm the controller takes over the workings of the boiler, so there is lots of scope for things going wrong.
My installer has done a sterling job of moving the boiler, which has included running pipes in a difficult route. The controller has been resited in the centre of the flat and the opentherm cable run to the boiler is just under 20 metres.
So the first thing I found was that once a Wise Hub has connected as OpenTherm, you are stuck with it. If OpenTherm is disconnected you can not then control the boiler using the relay. Apparently there used to be a selection and a status for type of connection in the App but they are no longer there. I put an inline switch in the opentherm cable so I could disconnect OpenTherm at will.
With it all up an running the hot water seems to be running at 60 degrees. If you turn the hot water knob on the boiler the value appears but you can not change it. The control has been over-ridden by OpenTherm. Sadly, as the Wiser does not send hot water temperature information you are stuck with 60 degrees. I did try powering up the boiler with OpenTherm disconnected, changing the tempurature to 40, and then connecting the opentherm. It immediately goes back to 60. 60 - 65 is recommended by Baxi to stop things growing in the pipes.
So there you go. There are two possible ways of adding control to the hotwater. One is to enter the world of Jiří Praus and his OpenTherm gateway Arduino Shield. You may need a degree in computer science and then you can insert the hotwater messages into the Wiser opentherm data stream. The device is here https://www.tindie.com/products/jiripraus/opentherm-gateway-arduino-shield/
The second possible way comes from a post I saw saying it has been known to work to add a two way switch in the OpenTherm cable and switch to a thermostat that can control domestic hot water. I found one, the EPH CP4M but have not tried it.
Finally, really it would be good if Drayton could add the DHW functionallity to the Wiser, also some indication that the Wiser hub was connected as OpenTherm and a way to switch it back to relay would be useful.
I will update this when I've had it going a while. It's June and the heating isn't really on.
UPDATE
I bought the EPH thermostat and replaced my OpenTherm switch with phono plugs so I could unplug the Drayton and plug in the EPH instead. And it works! I now have DHW at 45 degrees! much more civilised.
Update Update 22/10/22
Still occasional schedules appearing from no where. One person commented this seemed to happen if the controller disconnected from wifi. Have not tested it.
Radiators can be quite noisey with rushing sound, especially if only one radiator being heated. One forum recommended opening all lock valves and that seems to have improved things.
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