OTGW does not receive messages from boiler

[Zepman]

I'm trying to connect an OTGW (V2.7, Nodo-Shop, P16F1847, firmware version 6.1) between a Remeha Avanta Ace 35c boiler and a wired Remeha iSense V30 thermostat. Messages from the thermostat are received by the OTGW, but messages from the boiler are never received (by the OTGW or by the thermostat). As a result, the thermostat gives error F203 (connection problem).

What I did so far to diagnose:
* Checked for broken cables. Nothing is broken. When I connect the wires between the thermostat and the boiler directly, the thermostat has no problem functioning.
* I (re-)installed the latest firmware, also after I used the diagnosis firmware temporarily (see further up ahead).
* I tested the power values, and all are within acceptable ranges. This testing procedure was used: http://otgw.tclcode.com/debugging.html#interface
* The test mentioned on the same page using the diagnosis firmware was performed (test #4). All timing values are 'OK'.
* I switched the polarity of the boiler and of the thermostat connections on the OTGW. Tested all four scenarios. None of the tested configurations made a difference.
* I enabled remote override support on the thermostat. This also did not make a difference.

A GitHub repository notes a configuration that is the same as mine (an OTGW, same boiler, same thermostat), which seems to work fine. This makes me suspect something might be wrong with my OTGW. For reference:
https://github.com/ebaauw/homebridge-otgw

If anyone has any ideas for further diagnosis, I would really appreciate if you could share them with me.

[hvxl]

You are the third person reporting this type of problem with a Remeha boiler recently. That's starting to become suspicious.

What did diagnostics test #5 report (with both thermostat and boiler connected)?

What happens when you have the thermostat and boiler connected to the OTGW, pull the plug of both the boiler and OTGW, power up the OTGW, start test #3 and then power up the boiler?

[Zepman]

You are the third person reporting this type of problem with a Remeha boiler recently. That's starting to become suspicious.

OK. I might need to take back my previous suspicions concerning that my OTGW might be broken, if the same situation was recently reported by others. I'll try to keep an open mind.

What did diagnostics test #5 report (with both thermostat and boiler connected)?

OpenTherm Gateway Diagnostics test #5 (Voltage levels) output:

Code: Select all

Power supply: 3.302
Reference: 1.480
Thermostat: 0.635, 1.883
Boiler: 0.000, 1.122

What happens when you have the thermostat and boiler connected to the OTGW, pull the plug of both the boiler and OTGW, power up the OTGW, start test #3 and then power up the boiler?

OpenTherm Gateway Diagnostics test #3 (Bit timing boiler) does not give any output in this scenario. For reference, I also tried #2 (Bit timing thermostat), which gives the expected output based on the received messages of the thermostat.

If I read the result of test #5 correctly, could it be that the OpenTherm gateway default voltage reference level of 1.472V falls outside of the boiler's minimum and maximum voltage range?

[edit]
I took a gamble. The voltage in the middle of the overlapping range of the thermostat and boiler is around 0.9V. I reconfigured the reference voltage of the OTGW to 0.96V. I now receive messages from the boiler and the thermostat. Let me know if you want me to test anything else.

[hvxl]

The fact that you got two voltage levels from the boiler showed promise. Changing the voltage setting would have been my suggestion as well.

How good are your eyes? Can you check what is written on R4? That's the SMD resistor circled in the image below.

opentherm-gateway.jpg (93.3 KiB) Viewed 2610 times

The two most likely numbers on there are 271 and 331. Yours should say 271.

[Zepman]

How good are your eyes? Can you check what is written on R4? That's the SMD resistor circled in the image below.

I don't know about my eyes, but my smartphone camera works surprisingly decent in subpar light conditions.

Resistor R4.png (21.77 KiB) Viewed 2584 times

The two most likely numbers on there are 271 and 331. Yours should say 271.

As expected and shown, it is 271.

[hvxl]

Thanks. Then I'm not sure what causes the low voltages from the boiler interface. Maybe variations in the components. I'll try to figure this out with the Nodo shop.

But at least your problem is solved with the adjusted VR setting. Or do you still have issues?

[Zepman]

So far it seems that I do not have any issues. If I have some, I'll report them here. Thank you for your help in diagnosing my issue.

Since two others have also reported something similar with (recent?) Remeha boilers, could it be that the issue is with the boilers and not the OTGW?

[hvxl]

It is possible that the boilers don't deliver quite the required amount of current for the high logical level. But that is difficult to check, because the line is normally at the logical low level and only goes high for 1ms at most.

Having said that, you may actually have a better shot than most to measure it. When you activate the backlight of the iSense, it switches to medium power, meaning a high logical level for the current. So, when you connect the iSense directly to the boiler and measure the current, you should see around 7mA, most of the time. Then when you press a button on the iSense, causing it to switch on the backlight, the current should go up to at least 17mA.

Note: I assume you don't have batteries installed in your iSense.

[Zepman]

Having said that, you may actually have a better shot than most to measure it. When you activate the backlight of the iSense, it switches to medium power, meaning a high logical level for the current. So, when you connect the iSense directly to the boiler and measure the current, you should see around 7mA, most of the time. Then when you press a button on the iSense, causing it to switch on the backlight, the current should go up to at least 17mA.

Note: I assume you don't have batteries installed in your iSense.

This test will take me some time, due to the need to take measurements on the line at the same time the iSense is connected and interacted with. I will get back to you about this.

There are no batteries installed in the iSense, so that should not muddle test results.

[hvxl]

Don't go to too much trouble if it is inconvenient. In the mean time I have done some measurements myself. I found that on the v2.7 boards the output of the opto-coupler is marginal at the lower range of the allowed current levels. The next batch of boards from the Nodo shop will have a different value for R4 to improve this.

Users who already received a v2.7 board and have trouble with the communication on the boiler side are advised to lower the voltage reference setting, like you did.