Noise during modulation

Hi, we have the baxi 830 combi using opentherm with tado and Drayton TRV's.
If radiators are balanced they all heat up properly and radiators are quiet until the boiler modulates down as it starts to approach the target temperature.

As soon as the boiler modulates down the longe rad for eg starts making a motor running noise. The only way of stopping it is to open the lockshield fully (which then will mess up the balancing)

Is the only resolution to leave the lockshields fully open? Where does the problem lie?


  • I found the same thing with a couple of my radiators......the only thing that actually stopped this happening was the removal of all 10 tado SRT's from my CH system is now quiet again.
  • Sounds like the opening and closing of the SRT's was messing up the flow.

    I had a similar noise when other Drayton TRV's closed. These issues seem to point to pump speed, Tado say "reduce pump speed to 2", however on many new boilers it's a variable/modulating pump so it can't be adjusted.