CH on when not expected (diverter valve seized?)

I noticed this issue a couple of times in Winter, but since turning CH off entirely (for summer) it is more obvious: My radiators come on when they're not supposed to (clock control has switch set to '0').

Having read around a bit, it sounds like the diverter valve (aka 3-way valve) has seized. I can find the part on-line easily enough, but I have no idea about fitting. Would the system require draining? I have just bought my first house so am keen to learn the basics.

Alex

Hi Alex

Your diagnosis of a faulty divertor valve is correct.
Both the store and the upstairs part of the central heating system need to be drained to replace the valve (often these are located at the back of the unit and can be a bit of a swine to get to the connections easily).

Hi,

Thank you for your response.

Over the winter I saw the problem again and caught the valve in the act: I removed the actuator and heard it spring the position it wanted to me, so clearly the actual brass valve was jamming.

I drained the system and replaced the valve and actuator with the Danfoss model the manual recommends (interesting it was a Sunvic model I removed). However I was unable to remove the nut or olive on the 'AB' (bottom) connection, so I just re-used it. I replaced the nut and olive on the other connections with the ones that came with new valve. What is the best practice for this? Olives can be a pain to remove, is it usually best to replace them, or use the ones already on the pipe from the old component?

Reason I ask is that when I refilled, the bottom valve was weeping slightly, though last check (this morning) it was ok.

I haven't actually tested the valve yet, as I've hit another problem which I'll post about separately (blocked cold fill pipe).

Cheers, Alex