The central heating has been playing up for a few days now. I can
manually run the system using the lever on the motorised valve. i took
the motor off the valve and checked it using the thermostat and it
seems to work fine, i have tried turing the valve and that is easy to
move. The main problem seems to be that when i turn off the hot water
through the day and just have the radiators on the will not work. Once
i switch the hot water to come on the system works fine until you want
the rads off then you have to turn off the hot water. I have replaced
the thermostat with no change to the problem. the only thing is how
much should the valve open and close is it around 20 degrees because
thats all mine turns with the motor i thought it should be more ?
Please anyone got any ideas ?
Thank you all in advance........

In an earlier contribution to this discussion,
Dirksdonuts wrote:

The central heating has been playing up for a few days now. I can
manually run the system using the lever on the motorised valve. i took
the motor off the valve and checked it using the thermostat and it
seems to work fine, i have tried turing the valve and that is easy to
move. The main problem seems to be that when i turn off the hot water
through the day and just have the radiators on the will not work. Once
i switch the hot water to come on the system works fine until you want
the rads off then you have to turn off the hot water. I have replaced
the thermostat with no change to the problem. the only thing is how
much should the valve open and close is it around 20 degrees because
thats all mine turns with the motor i thought it should be more ?
Please anyone got any ideas ?
Thank you all in advance........

I assume that you have a Y-Plan system - fully pumped, with a 3-port
mid-position valve, designed to provide HW only, CH only, or both together?
[See http://content.honeywell.com/uk/homes/systems.htm and scroll down to
Y-Plan]

I assume from the fact that it has been playing up for a few days that it
*did* work properly prior to that? This is important, because there are lots
of ways to wire up Y-Plan systems wrongly, and only one way to do it right!

Assuming it *has* worked ok in the past, you almost certainly have a problem
with the 3-port valve - or more likely with its actuator. The valve is
supposed to turn through 90 degrees between HW and CH - with the "both"
position being mid-way at 45 degrees. The manual lever only moves the valve
to the mid-way position.

It sounds to me that the motor is only moving it to the mid-way position
when it should be moving it all the way to CH. This would explain why the
boiler and pump only run when the HW is also on - because the valve never
gets far enough open to operate the microswitch which provides an
alternative supply for the boiler and pump.

I would recommend replacing the actuator - making a careful note of the
wiring before disconnecting the old one, and connecting the new one
*exactly* the same. [You *can* buy the internal bits (synchro motors,
micro-switches, etc.) and effect a repair - but it's a bit fiddly, and
safer - in my view - to replace the whole thing].
--
Cheers,
Set Square
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Thanks for the fast reply setsquare it looks like i will be off to find
a new actuator first thing in the morning.

Thanks for the fast reply set square it looks like i will be off to
find a new actuator first thing in the morning.