central heating full blast, regardless of setting...

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

Reply to
nealegoogle
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It sounds like you've got a fairly standard Y-Plan system - so your wiring should look something the Y-Plan diagram in

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- 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.

Reply to
Set Square

Set Square,

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

Best wishes,

Neale

Reply to
nealegoogle

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