I used a 11 pin plug in relay rated at 10 amps because that is what I had. If I was to purchase one think I would go with the interface type http://uk.rs-online.com/web/p/interface-relay-modules/6237236/ as they are a slim profile, maybe have a look on ebay for a cheaper one, you are only...
Just bought a new house that has the Drayton zone valves fitted to the HW & CH circuits and found the same problem. The actuator shuts but the pump and boiler run, the water flow goes through a bypass valve and the water is pumped around the loop and controlled by the boiler stat until the zone...