NEST Thermostat boiler firing up randomly and turns off when I turn 'on' bacteria protection

[Amy25]

I recently had to get my diverter valve replaced.  Since then I have been having issues with my boiler randomly turning on when it shouldn't.  I restarted the nest thermostat (3rd gen) a few times and to see if this solved the issue and it hasn't.  I also checked whether bacteria prevention was turned on and it wasn't.  However, I have experimented with turning bacteria prevention on and it actually stops the boiler from firing up.  Could this happen?  Is this a problem with the nest thermostat or the way that the electrician left my 3 port valve.  Is there something they did that could be causing it to act in this way?  

To confirm, I have no pre-programmed heating times in my nest thermostat, i.e. the boiler should only fire up when I manually turn it on.  

[Frustratedddd]

This is an odd one! The Bacteria turned off and no heating schedule, the thermostat is just like a switch but tempreture controlled. That being, you turn the dial clockwise and it calls for heat rads/boiler comes on, anticlockwise rads/boiler off. Simple as that really.

Ther might be a glitch, and I would suggest rather than restarting, do a full settings reset. This will erase everything, and take you back to factory. Obvioulsy you will have to set the stat up again, but no big deal if you have nothing setup.

[Amy25]

I have done a full settings reset about five times now and it makes no difference, unfortunately. 

[Frustratedddd]

How exactly did you do the full reset?

Are you a system boiler or Combi?

I think this could be an install issue in that case with the valve.

[Amy25]

I did a factory reset on the nest base unit and forced a restart on the heat link.   I have a system boiler. 

I just had the company round that replaced the 3 port head.  They checked the wiring and believe they have now fixed the issue.  They said the problem was as follows:

The cylinder stat was incorrectly wired and that the common and unsatisfied wires were the wrong way round.  

[Frustratedddd]

Good to hear you back up and running, and as for the person that fitted the valve, well what can I say! Skills today are very poor, and very sad they left you in that position.