Hello,

I've been abroad for the last 3 years, and have come back to find that
my gas-powered central heating system is behaving badly. Regardless of
the timer or room thermostat setting, hot water is sent around the
house to all the radiators whenever the boiler is running. Obviously
this makes the house very hot, so I've been turning off all the
radiators as a stop-gap.

While I was away, a new boiler was installed, so my best guess is that
the wiring has not been done properly. The various wires meet at a
12-port junction box but I don't have a wiring diagram except for the
"programming wiring guide" supplied with the Landis & Gyr MAV 322
return motorised valve (and that features a 10-port junction box
anyway).

The control system is a "fully pumped, mid position" one.

Any advice would be appreciated.

Sincerely,

Neale

In an earlier contribution to this discussion,
nealegoogle@mac.com   wrote:


> Hello,
>
> I've been abroad for the last 3 years, and have come back to find that
> my gas-powered central heating system is behaving badly. Regardless of
> the timer or room thermostat setting, hot water is sent around the
> house to all the radiators whenever the boiler is running. Obviously
> this makes the house very hot, so I've been turning off all the
> radiators as a stop-gap.
>
> While I was away, a new boiler was installed, so my best guess is that
> the wiring has not been done properly. The various wires meet at a
> 12-port junction box but I don't have a wiring diagram except for the
> "programming wiring guide" supplied with the Landis & Gyr MAV 322
> return motorised valve (and that features a 10-port junction box
> anyway).
>
> The control system is a "fully pumped, mid position" one.
>
> Any advice would be appreciated.
>
> Sincerely,
>
> Neale


It sounds like you've got a fairly standard Y-Plan system - so your wiring
should look something the Y-Plan diagram in
http://content.honeywell.com/uk/homes/systems.htm - although that also uses
a 10-way junction box (but only actually uses the first 8 ways). If your box
is different, you need to determine what is connected to what - rather than
worrying about which terminal number it uses.

It *could* be wired wrongly - but it's more likely either that the actuator
has got confused or that the wet part of the valve is physically jammed in
the mid position and not allowing the spring to return it to the HW-only
position. The first thing to do is to remove *all* power from the system -
which means turning it off at the FCU, *not* at the programmer. If the FCU
isn't near the mid-position valve, you need to get someone else to turn it
off while you listen to the valve. You should hear the spring return moving
it to the HW position. If it does, it may then work ok when you turn it on
again - it's worth a try.

If nothing happens, you need to look further. I'm not familiar with L&G
actuators, but if it's similar to other makes, it should be possible to
remove the actuator from the valve proper by undoing a couple of screws. If
the actuator returns to the CH position when removed, but not when attached,
it's a pretty fair indication that the valve is seized. You should be able
to rotate the shaft of the valve through plus and minus 45 degrees either
side of the mid position with very little effort - either with fingers and
thumb or with *light* pressure using pliers.

If the valve *is* seized, you *may* be able to free it by turning it to and
fro with pliers - otherwise it will need replacing, which will involve a
partial drain-down of the system.
-- 
Cheers,
Set Square
______
Please reply to newsgroup. Reply address is invalid.

Set Square,

Thanks! I'll give this a go, and see what happens.

Best wishes,

Neale