HW comes on with CH - Wiring?

[Echo the husky]

If only everything was that easy!!

 

[jcwacky]

Hmm, spoke too soon. Discovered an unintended side effect: If the HW is OFF but the Boost button on the cylinder thermostat is pressed (and the cylinder temp is below set-point), the boiler will fire up and try to heat to cylinder, but it seems that instead of heating the cylinder, it's heating the radiators, causing the house to get hotter and hotter until the boost is manually canceled.

Is there an easy and obvious fix for this?

 

[jackthom]

The boost button won't work correctly in a system with a properly wired 3 port valve. Unless the valve is already in the heating off position when you push the button you won't get the effect you want.
It will give either heating only or both heating and hot water.
It is possible to get it working with the addition of a relay which when triggered by the button drops the HW OFF connection.

 

[jcwacky]

The boost button won't work correctly in a system with a properly wired 3 port valve. Unless the valve is already in the heating off position when you push the button you won't get the effect you want.
It will be either heating only or both heating and hot water.
It is possible to get it working with the addition of a relay which when triggered by the button drops the heating ON connection.

Ok, thanks for confirming Jack. The programmer also has a boost button which should still work, so I can just make sure to use that one!