In an earlier contribution to this discussion,
wrote:

Hello all,

My continuing struggle with my heating system goes on. I recently
replaced the heating pump and some valves, and the banging when the
boiler started up has gone away. So that advice was very good.

However, there is still the problem that the radiatiors get hot
whenever the hot water comes on, even when the central heating is set
not to come on. The setting on thermostat downstairs seems to have no
effect at all.

I guessed it was the 3-port motorised valve (Landis & Gyr MAV322).
Removing the cover I noticed that the motor would not turn to the "B"
setting, it sort of got halfway and just clicked. Looking further, I
found that one of the two microswitches on the circuit board seems to
be broken. Presumably this is the problem with the valve? And if that
is the issue, replacing the microswitch (or the whole valve) should
fix the fault, surely?

However, even when I jam the valve at the B setting, which should send
all the water to the cylinder, the radiators still get hot.

So I'm stumped. If the valve is broken, then why doesn't forcing it to
the B setting stop the hot water going around my central heating
system?

Many thanks!

Neale

I'm not familiar with this valve - but, assuming it works in the same way as
other mid-position 3-port valves, the B (HW) position is the 'rest' position
to which the valve returns by means of its return spring when the motor is
not energised. So I don't understand about not being able to motor it to the
B position.

Is this is new problem since you made changes to the system. Are you *sure*
that this valve is installed the right way round, and wired correctly, in
line with the Y-Plan wiring diagram? [See
http://content.honeywell.com/uk/homes/systems.htm and scroll down to Y-Plan.
I'm assuming here that L&G kit works in the same way as Honeywell.]
--
Cheers,
Roger
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