Tado and Vaillant EcoTec

Recently I have replaced my boiler with Vaillant EcoTec plus vcw 346. It is connected to my tado thermostat via ebus. It seems to be working in that when the thermostat calls for heat the boiler switches on and starts working. The problem is, whatever the temperature in the flat is and whatever is needs to be the boiler always switches on on the lowest end of power modulation. This means it can never reach the temperature I want. If at 4 am when the boiler goes on I have 17 degrees by 8 am I will have 18.6 (target being 21). I don't know if the boiler or the thermostat is the problem. The guy who installed the boiler was not familiar with tado.

Any ideas as to what is going on?


  • You might need to increase your max flow temp on the boiler or check that your radiators are balanced. With Tado on boost, does one get hotter much quicker than the others from cold?
  • Thanks! radiators are identical save for a couple of tower rails that heat up the bathrooms much quicker. This was not a problem with my old Bulex boiler. All radiators haver tado TRV so I guess they should be balancing through closing them. Also the boost part is odd. If I put it on boost I do not see my boiler doing anything new - the power is still at some 20%. Finally, since the boiler and tado are connected via ebus, isn't tado setting the temperature of the water on the boiler. In any event, I have it on 65 degrees Celsius so this should not be a problem.

    It has been days I'm trying to figure this out and it is killing me.

  • It sounds like a boiler config issue - when you put on boost it should be telling the boiler to produce close to maximum output.
  • Is the partial load on the boiler set to 'auto'? That caused a lot of problems when my ecotech 835 plus was installed (using a relay thermostat).