Hi,
Please could someone help. I'm having problems with central heating / hot water system in that the hot water just gets hotter and hotter when either hot water or central heating is on.
I suspect the thermostat on the cyclinder...
Hi rob that makes two of us I reckon you have a problem with the stat and/or wiring too
A quick description of how it works
hotwater only
A call for heat from the programmer will provide power to the boiler via the cylinder stat when the HW is up to temp then the stat will toggle over to satisfied and remove power to boiler, when it cools down it will toggle back and refire the boiler as necessary
the valve plays no part electrically when on HW only
hotwater and central heating
now the valve comes into play,the boiler will be operated via the cyl stat as above but now the CH call will open the valve by providing power to the valves white cable
where the valve opens to depends on what state the cylinder stat is in,but for now we will persume that the cylinder stat is still calling.
so the cylinder stat is still calling and there is power on the valve white,so the valve opens, when it reaches half way (mid pos) it toggles over the first micro switch which switches in a resister/diode arrangement which modifies the ac waveform supplying the motor and stalls it
so now we have the valve open mid position and the boiler is still being controlled via the cyl stat
now two things can happen
1)If the room stat becomes satisfied then power is removed from the white and the valve returns to the Hot water position again,blocking off the heating port
2) if the cyl stat becomes satisfied then it will toggle over to the satisfied terminal which is also connected to the valve grey this restores the voltage to the motor and drives it to the heating position and blocks off the hotwater port
this is where the second microswitch comes in,remember that the boiler was being supplied via the cyl stat,this power is removed when the stat toggles over,so now the boiler is fed from the roomstat via the second microswitch which is connected to the valve orange
if the room stat becomes satisfied it now just removes power to the boiler as apposed to blocking off the heating port because the power on the grey holds it in this position
if the cylinder stat calls for heat then power is removed from the grey,the valve winds back till it hits the first microswitch which then stalls it again at mid point if there is still power on the white(due to the modifyed dc waveform)
on selecting CH only the valve is fooled in to thinking that hotwater is always satisfied by providing power on the grey when hot water is switched off and operates as described above
so basically (omiting earth and neutral)
white=drive to mid
grey= drive to heating only(will only work if power is on white and at mid but will also hold valve at heating once there regardless of power on white)
orange=connects to white when valve in heating pos and used to operate boiler(heating position only)
hope I have explained it ok
Matt