Nest Thermostat (G4CVZ) with Bosch Condens 3000 w + COMPUTHERM Q3

Hofi — Tue, 20 Sep 2022 13:56:15 GMT

Hi All!

I'd like to replace my old COMPUTHERM Q3 thermostat (http://manuals.calorsol.de/manuals/English/COMPUTHERM_Q3_ENG.pdf) with my new Nest Thermostat (G4CVZ) and controlling a Bosch Condens 3000 w gas boiler + heater (https://gepesz.hu/connect/dokumentumok/cikkfile/uj/inst_bosch-condens-3000w-6720816792_20170719_1657.pdf) (I'm in Europe, Hungary)

Yes, I know, the COMPUTHERM Q3 is a 230V switcher device, but the documentation of the Bosch Condens 3000 w (page 29. and 14.) is referring to other 24 Volt thermostats that also can control the heater (e.g. Bosch TR100, TR200 https://www.hasznalati-utasitasok.hu/bosch/tr-100/haszn%C3%A1lati-utasit%C3%A1s?p=90)

Both TR100 and TR200 documentation (page 90.) show that using those thermostats one should simply connect no. 1,2,4 connectors of the thermostat to the no. 1,2,4 connectors of the heater ST19 (page 29) respectively and that's all.

Unfortunately, I could not find any more details about what the mentioned 1,2,4 connectors are exactly but I figured (measured) out that

(1) - is the (C) common wire
(4) - is the (R) power wire

so I guessed the (2) should be the (W) heat control wire.

According to this, I wired my Nest Thermostat that has now correct 24V power (it is confirmed by the Nest device itself as any other combination of 1,4 connections led to error and/or 'No Constant Power' messages on the device)

So I was happy till that point seemed everything will be fine, but unfortunately, it is not the case :S

Even though when I put the Nest Thermostat into Heat mode I can see that (2) wire (W) gets a ~24V power, but it has no effect on the heater at all, it does not turn on the heating.

Could any of you please point me in the right direction what can be the problem here?

Thank you in advance!

Re: Nest Thermostat (G4CVZ) with Bosch Condens 3000 w + COMPUTHERM Q3

Bence — Sun, 29 Jan 2023 11:08:09 GMT

Hello

you need EMS to OpenTherm adaptor and you need HeatLink adaptor as well

Bence from Hungary

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Nest Thermostat (G4CVZ) with Bosch Condens 3000 w + COMPUTHERM Q3

Re: Nest Thermostat (G4CVZ) with Bosch Condens 3000 w + COMPUTHERM Q3