Honeywell st669 to st9400c

[RandomGrinch]

So just to fully understand, with my st699 when I turn the heating on the hot water was always on?

Yes, that's how it has been wired up.

 

[rumel1993]

You are correct, just checked. Can’t believe I did not notice that. Tbh when I turn the heating on 90% I turn the water on at the same time. So that’s prob the reason why I never noticed.

Temp for C/H

Temp for hot water

 

[DP]

I can confirm it’s a gravity system. A engineer has mentioned this in the past when we got the boiler serviced.

So just understand in simple terms the programmer is not compatible in the way I want it set up.

Thanks

Alternative. Fit a cylinder stat to give you operation that 699 gave.

 

[DP]

Just tried the Mini program mode no luck hot water is on when central heating is on.

I’ve plugged the old program (st699) as it only the timer that stop working properly on it. until I figure a way around this.

I really appreciate the help guys, thank you

On a gravity hot water system, it is the hw channel that only fires the boiler and ch channel that only runs the pump.

When you ask for hw, boiler fires and heats the water in the cylinder to boiler stat temperature.
In present situation for ch the pump is running but boiler is not firing because that is a function of HW channel.
On 699 this was achieved by clever wire links. On some programmers like Danfoss FP there is a gravity setting.