Hi, My Keston c25 started misbehaving by coming on at odd times of the night when it should have been off. Now it is on all the time, even when the controller has the HW and CH off. I've replaced the controller (it was old) and the 3-port valve top to no avail. My conclusion is that the boiler is switching on when it receives a 100v signal from the Y-plan valve on its switched live whereas it should only switch on when this line goes to 240v.
Anyone else had this problem? Any solutions?
Tony
It has a built-in frost stat. Could that have triggered it? Have you got an external froststat fitted anywhere?
Again, froststat?
I'm not intimately familiar with Y-plan, but I would not assume sensible operation if the call for heat input is drifting to strange voltages.
Can you use a 100k pull-down resistor to remove the strange voltage?
Checking with the Keston info, I see the boiler is supposed to need
190v min on the control live terminal. The y-plan arrangement does mean that it's normal to have a rectified AC supply (through a big resistor) on the control wire in certain positions. I suppose a pull-down resistor would do the trick. Tony
I fairly certain that a correctly installed Y plan control system will send a solid 230Vac nominal to the demand input of the boiler. Internally the 3 port mid pos valve may use weird stuff but externally it normal mains ac.
Try confirming the demand signal with a (filament) light bulb.
ISTR you get a shitty signal when the valve is mid-position. I tried to make it drive a mains relay when I was designing my system, but it buzzed in one of the positions with half-wave rectified mains on it. In the end, I didn't use the switch output from the valve.
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