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davesparks
So I have noticed that it's slightly different to how I described before:
1. If I turn on just HW then the valve moves to just HW I get just HW and it heats the cylinder.
2. If I turn on just CH the valve DOES move to the CH position, but even if the the room thermostat is set above the room temperature the CH DOES NOTcome on.
Strangely - if I am in scenario 2 above - with the CH switched on and the valve in the CH position, if I turn the HW on as well then the pump kicks in and the boiler starts up - the weird thing is the valve does not move into the middle, dual CH and HW position - it stays at the CH position and the rads heat up. This does not seem to heat up the cylinder (which is fair enough as the valve position is in CH only for some reason).
In the above scenario, once the room comes up to temperature the signal goes to the controller to turn the CH off (obviously the CH light is still on in the controller as the timer is on CH) - it's just got the signal to stop as the temperature is up. When this happens the valve moves to HW only and then it heats just the cylinder.
If I then put the room thermometer back up it moves into the dual position and heats both.
So I still have the same problem of the CH not coming on by itself...
So to me the really weird thing is:
1. The CH not coming on by itself, yet the valve is moving into position and so thinks it should come on.
2. If the CH is supposed to come on and the controller has a green light and the valve is in the CH position - if I then ALSO then put the HW on, both lights on the controller are on, but the valve does not move to the dual position and stays in the CH position heating just the rads.
Then I think we can go back to my original suggestion of the microswitch in the valve being goosed.
This microswitch gives the boiler the signal to fire once the valve has moved to the CH position.
There is not a CH 'off' signal in the system, you only have a DHW off signal.