Ideal Combi2 Opentherm Error "Room Thermostat Fault (65)" & "Check Room Stat Batteries"

edited September 11 in General Questions & Topics

After a very unproductive and frustrating session with tado support I'm hoping I might get some help from the forum.

I've a new (2-3 months) ideal combi2 boiler and I've swapped my original extension kit for the EU one to get Opentherm.

In testing it all works nicely, and being the summer the boiler has mostly been in Summer mode with the CH turned off. HW works as expected (50 degrees 24/7) and responds to temperature changes within a few minutes.

Problem - I've turned on the HW and rapidly accumulated 391 faults in the boiler log "Room Thermostat Fault (65)" which display on the boiler as "Check Room Stat Batteries" when the error is active. Best I can work out seems to be the extension kit reporting a fault over the opentherm bus.

I think there might have been a clue in the chat. I have one TRV that has poor connection and this morning when I noticed the error on the boiler that TRV was offline. What confuses me is that this TRV is not assigned to a zone controller. I can see arguments both ways for why this might be causing my error but also why I might expect it not to feature in the issue.

Frustratingly tado support either can't or won't confirm either point, simply bouncing between boiler fault refer to boiler manufacturer, or that I need a tado installer to review and then contact them for support.

Has anyone else seen this error before and hopefully identified a solution? Or any insight into where to direct efforts towards a resolution?

In the short term I've removed the offended TRV from it's usual location and am actively monitoring the number of errors logged in the boiler. After that I guess I start removing TRVs from my account til hopefully the errors stop accumulating


  • What do you mean by you’ve turned on the hot water? I’m assuming you have a combi. You should have a hot water temperature control with an Opentherm combi, not an on off button.
  • Apologies typo. Should read "Problem - I've turned on the CH and rapidly accumulated 391 faults in the boiler log..."

    (For completeness, re HW I have both on/off AND temperature control. If off in tado, then the boiler defaults to 55. If on in tado then tado sets the temperature and you can apply a schedule.)

    Back to the CH issue. I removed all TRVs from my account and swapped the opentherm cable for a shielded one. This reduced daily logged errors to 1 per day. Yesterday I readded all TRVs and overnight have gained 12 logged faults on the boiler.

    I've come to the conclusion that tado and Ideal aren't quite "talking" right over the Opentherm interface. I assume if I had access to the logs on the tado side I'd find a similar number of errors but there doesn't seem to be any way to achieve this short of an additional module (something like Opentherm Gateway? to log the traffic.

    Bottom line. Neither tado support nor Ideal are interested in helping, and everything seems to functionally work so I guess it's not a problem. If it does become a functional problem I can swap tado to relay mode in about 10 mins while I look for replacement options.

  • I can’t really help much but fwiw Tado works fine with my ideal vogue over Opentherm. I don’t usually have connection problems with the TRVs though. I’d be surprised if ideal has changed its Opentherm implementation but I suppose it’s possible.