What system do I have?

[ianmcd]

No when you select HW power goes to your boiler and it fires and the water circulates to the cylinder through natural gravity, when you select CH power goes to the pump which circulates the system water through your radiators, the HW is still getting hot as you cant control this or the boiler would go off, if you wanted to have CH without HW you would have to change to a fully pumped system and with your boiler a complete waste of money

 

[DP]

As said by Ian, for hot water, boiler fires, heated water circulates by convection

When you select CH, pump runs but boiler will not fire unless your programmer can also power up HW zone that fires the boiler

To make your system work with hive, you will need to replace existing programmer for one that has C, NO and NC contacts or use a relay to fire system forgot water. Hive will the allow you to do its magic

You do not need a new boiler, just better controls and configuration

 

[Zilla]

So Hive not nest then?

I gave up on nest as I couldn't work out how to make it send power to the boiler only when I wanted HW, but to send power to the boiler and pump on CH mode. Unless when you run through setup you can tell it that you have a gravity fed HW so it knows to send a fire to the boiler via HW.

 

[ianmcd]

I really dont recommend that you fit any of them but if you really want to do it you will have to set whichever one you decide to use , you will have to set the HW on at the same time as you have your CH set to be on you will never get CH without HW and if the HW is not calling for heat the boiler will not fire