SIEMENS RWB9

[thekilljoy]

My central heating has developed a problem in that when I apply mains power to the system but with both the HW and CH switched off (lights out) the boiler fires up and activates the pump and central heating. I cannot switch off the heating.

 

[muggles]

Zone valve microswitch stuck on

 

[thekilljoy]

But why does it trigger the boiler ignition when both CH and HW demands are switched off?

 

[CBW]

It has a permanent live and a switched live, so basically the switch is stuck in the on position, leaving it connected, whereas your programmer would normally remove the switched power from the zone valve, the output side of the valve is receiving power because the switch is stuck open.

 

[muggles]

Because that's how they work. Programmer activates zone valve motor, which opens the valve and presses a microswitch. The microswitch contact sends power to the boiler, which fires up. If it's stuck open, it'll power the boiler at all times because the microswitch is continuing to send power to the boiler even with the programmer off

 

[thekilljoy]

Makes sense, I assumed that the controller just caused valve to move. So is it just a case of having the microswitch replaced without touching the actual mechanical valve itself.?

 

[CBW]

Usually depends on zone valve, and whether you can solder the microswitch, probably better just obtaining a valve head.

 

[thekilljoy]

Having checked the valve.

The CH valve it is open and the lever is floppy irrespective of whether or not there is power applied to the system. Does this mean it is just motor, needless to say it is in an incredibly awkward position and I hope it is not necessary to change the whole head.

 

[ianmcd]

Having checked the valve.

The CH valve it is open and the lever is floppy irrespective of whether or not there is power applied to the system. Does this mean it is just motor, needless to say it is in an incredibly awkward position and I hope it is not necessary to change the whole head.

yep the motor will have seized

 

[thekilljoy]

As I said it is in an awkward place so although the motor replacement looks straight forward I will probably get someone to do it who has done it before and has double jointed fingers.

 

[ianmcd]

As I said it is in an awkward place so although the motor replacement looks straight forward I will probably get someone to do it who has done it before and has double jointed fingers.

post a pic of where it is located