Heating Only not working

[Matthew Bailey]

Hi,

I can not get my central heating to work in "heating only" mode. I do not know if this has ever worked as I just moved house. (House is approx 15 years old and most of central heating components have been replaced in the past 5 years I believe.)

It works fine in "Hot water only" or "both heating and hot water" but when I just turn on the central heating at the programmer nothing happens.

The programmer is new (Tempus 7).

I suspected the 3 way valve was faulty so I changed this for a new one, (Danfoss Randal H3A) Initially I just fitted the new actuator, but then fitted a new valve with the new actuator. This didn't make a difference.

When the programmer is set in "Heating Only" mode I am able to use the manual override switch on the 3-port valve and then the heating comes on. (The water also comes on as the valve is in the mid position when using the manual override switch.)

I did start to attempt to make a wiring drawing of the whole central heating electrics, but so far this is proving to be complicated as I can not confirm exactly which cables are which at the junction box in the airing cupboard.

One thing I did note is that on the programmer only the outputs for Hotwater On and Heating On are connected. Hotwater Off and Heating Off are not used. Is this significant?

Any suggestions where to start looking?

Thanks,

Matthew

[Set Square]

You have a wiring problem. This configuration *only* works in CH-only mode when the HW-off terminal in the programmer is properly wired up. In addition, the cylinder stat *must* be of the changeover rather than on/off type. [You don't need a CH-off connection]

Have a look at the Y-plan wiring diagram in

and bring your system into line with it.

[Lurch]

On Sat, 27 Nov 2004 17:19:02 -0000, "Matthew Bailey" strung together this:

Yes, it's wired wrong. Here's a wiring diagram.