Hi All,

Wondering if someone more knowledgable than myself can give me their opinion?
I have a Honeywell Sundial Y plan heating installation which utilizes a 3 port midposition valve. I currently have a problem where my rads are still giving of heat when the CH is set to "off". It seems to me from a little investigation that this is being caused by convection through the 3 pos valve. I have removed the valve cover and observed the motor functioning correctly!
Can these valves fail machnically whilst the motor still works? Would the simplest coarse of action be to replace the entire valve assembly?

Any comments and suggestions will be gratefully received.

Forgot about this:

Before I removed the cover and checked the valve I cycled the manual lever a couple of times.
I'm keeping an eye on things but I think the valve might of been seized and using the lever has free'd it up.
Wish I'd check the valve before doing this and then I know for sure.

Well I've been watching the system to see what its doing and the problem is still there. The rads closest to the hot water tank are all hot even though the CH is off. If I manually move the valve to the A position (HW only) it cycles back to the A+B position even though the CH is off (the pump is running as it should e.g. it is off whilst the CH is off and the HW is up to temp).

Can a 3 position valve fail in this way?

In an earlier contribution to this discussion,
matthewh wrote:

Well I've been watching the system to see what its doing and the
problem is still there. The rads closest to the hot water tank are
all hot even though the CH is off. If I manually move the valve to
the A position (HW only) it cycles back to the A+B position even
though the CH is off (the pump is running as it should e.g. it is off
whilst the CH is off and the HW is up to temp).

Can a 3 position valve fail in this way?

I've never known an actuator drive itself to the A+B position when there's
no CH demand. Sounds more likely that there's an external wiring fault. Has
it ever worked properly?

I have occasional known actuators to get 'confused'. The way to reset it is
to turn off *all* power to the heating system for a minute or so. You need
to do this at the FCU which feeds the system - *not* at the programmer 'cos
that would still still leave one connection live.

With all power off, the spring return should bring the valve firmly to the
HW-only position. If it doesn't, either the mechanical part of the valve is
stuck or the spring return isn't working properly.

With the actuator removed from the valve, you should be able to rotate the
spindle of the valve with finger and thumb - or at any rate with *light*
pressure with a pair of pliers.

You can put the actuator through its paces while it's off the valve by
selecting all possible combinations of CH and HW in turn, and making sure
that the actuator moves to the correct position in each case. [Put the
spindle in the A+B position while you do this].
--
Cheers,
Set Square
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