2 port Zone vale CH system query

[ajb99]

I wonder if anybody can assist with a query.

I have a fully pumped CH system that uses 2 two port zone valves with the usual dual timer (tempus7) and room and cylinder thermostats.

The system is wired so that for both the room and cylinder there is the timer and thermostat in series this drives a 2 port, spring return, valve and the axuillary micro switch drives in a seperate circuit to the pump and boiler.

If this axillary switch fails (as mine recently did, due to a leaking valve) in the on position then no matter what the timer and or thermostat is set to the boiler and pump will fire up as this is an independent circuit.

My question is could this axilary switch be in series with the timer and thermostat so that all 3 need to be made (on) before the boiler/pump come on or is there a good reason why this is not done. Most circuit diagrams show the axillary switch on the zone valve as a seperated circuit to drive the pump/boiler.

Thanks

 

[doitall]

The oranges all has to be common to operate the boiler and pump.

 

[stem]

Is there a good reason why this is not done. Most circuit diagrams show the axillary switch on the zone valve as a seperated circuit to drive the pump/boiler.

Yes, there is a good reason. Electrical Isolation.The fact that both valves have a microswitch inside means that either the hot water or central heating can be on without effecting the other. The shared components boiler & pump, are operated by the microswitches so are electrically isolated from the valve circuits.

Do what you suggest and the hot water and central heating fuctions would 'back feed' each other via the boiler.