Zone valve not closing tightly?

[f0rmula]

I've got a couple of these, controlling a upstairs and downstairs zones:
http://www.screwfix.com/p/siemens-czv222-2-port-zone-valve/77334

I'm using them manually at the moment, as I've not wired in the thermostat/timer just yet. I'm just about to. I notice that when they're closed, the radiators in the zone that's supposed to be off slowly get hot. There's obviously some flow still getting through.

Is that to be expected? Should they not be a reasonably tight seal? When they're actually powered, would they seal any tighter? They seemed to just close via a spring, so I didn't think they'd use the motor to close when powered.

Maybe I should have just shelled out for some Honeywell ones :-/
http://www.screwfix.com/p/honeywell-v4043h-2-port-motorised-valve/31480

 

[hazetimesfive]

are they installed the right way round? is the system cruddy?

 

[plummerman]

Are the motor open or motor closed valves? Obviously the later is held closed by the motor so could be the reason you still have flow....

Or some crude on your seatings allowing flow

 

[stem]

If you have recently installed them, are they in the correct location? If not you may be suffering from 'reverse circulation'

If you're not sure what it is, ChrisR produced a great diagram explaining reverse circulation. You can find it in the link to another post here.

 

[f0rmula]

are they installed the right way round? is the system cruddy?

They're the way round the manual says they should be. The system is new.

Are the motor open or motor closed valves? Obviously the later is held closed by the motor so could be the reason you still have flow....

Or some crude on your seatings allowing flow

They're spring return valves, so i think they fail closed. I guess that means the motor won't close it any tighter than the spring does.

If you have recently installed them, are they in the correct location? If not you may be suffering from 'reverse circulation'

If you're not sure what it is, ChrisR produced a great diagram explaining reverse circulation. You can find it in the link to another post here.

The heat is coming from the flow, not the return, so i guess it's not reverse circulation.

It feels to me like the spring return just isn't strong enough to hold the valve shut, or maybe there's crud on the seatings. Either way, sounds like connecting up the power isn't going to help me and I'm reduced to at least replacing the motor or dismantling the whole valve.

 

[CBF]

as it's a new system where is the return from the cylinder connected into ? if the ret cylinder connection isn't last last one going back to the boiler then the rads could be getting warm when the hot water is on

 

[f0rmula]

as it's a new system where is the return from the cylinder connected into ? if the ret cylinder connection isn't last last one going back to the boiler then the rads could be getting warm when the hot water is on

Sorry, i didn't state. it's a combi boiler.

 

[ianmcd]

have you installed a system by-pass before the valve positions ? doing so may solve your problem