Unable to correctly connect Honeywell ST9100S

[drdr]

I purchased a Honeywell ST9100S. A simple single day timer ideal to replace my old Switchmaster 805 programmer that recently packed up. The Switchmaster originally controlled the heating and water but was later changed to operate the hot water only, the central heating is now controlled by a programmable thermostat.

I have spent days trying to get the wiring for the ST9100S to work and cannot. The timer is either overridden or takes over the central heating as well as the hot water. There are only so many possibilities but I can’t find the right one.

Can anyone tell me how the ST9100S should be wired? I want the clock to control the hot water and the central heating to powered but operate independently. There is a Boiler Service facility which I do not want to use.

I have attached details of the old Switchmaster wiring and the wiring diagram for the ST9100S. Honeywell say they cannot help.

Any suggestions will be gratefully received – I am getting desperate!

 

[jackthom]

Do you have a hot water cylinder and a 3-port valve or similar in the system?

The ST9100S can't provide both the DHW ON and DHW OFF signals that your diagram suggests you may need to control such a valve.

 

[drdr]

yes it does - what you say could explain a lot. can you suggest an alternative device that would do the job?
Thanks for your reply.

 

[jackthom]

I think you will need to buy a 2 channel programmer, even though you won't need to use the central heating side of things. That way you are guaranteed to have all the correct control signals.

Maybe something like this Honeywell

http://www.plumbarena.co.uk/product...gclid=CLGB05avscICFcrKtAodYjgAoA#.VILwA8kud3U

http://www.honeywelluk.com/Documents/Installation-Guide/pdf/835.pdf

 

[D_Hailsham]

The ST9100S is not suitable. You need either the ST9100A (24hr) or ST9100C (7day). These are single channel timers; you don't have to buy a 2 channel programmer.

The S version is intended for rental properties where the boiler has to be checked annually. It has a facility to set when this has to be done and will turn the boiler off if it's not checked in time. The wiring is completely different from the A and C versions.

Did you buy the timer off Ebay?

 

[drdr]

D_Hailsham - yes I did buy it from ebay. Basically I wanted to get an electronic timer (the old switchmaster was noisy) which I thought it more than adequate to control the hot water twice a day, I had not considered the diverter valve which jackthom brought up. Since you can program out the service facility I thought it would do the job.
From what you say I feel that you think it might be unsafe to buy from ebay (even if stated to be new?), and you are confident that the ST9100A or C will work. I do not want to buy another that is unsuitable.
Unfortunately I am neither a heating engineer or an electrician. Just the average DIYer grateful for guidance.

 

[jackthom]

D_Hailsham is right, the ST9100A and ST9100C have double pole relay contacts so will provide signals for both HW_OFF and HW_ON.

http://www.honeywelluk.com/documents/Installation-Guid/pdf/833.pdf

 

[drdr]

Thank you all so much for your help. I will purchase the ST9400A, it is the most basic but does all that I need.
Hopefully this one should work.
Will let you know the outcome
Thanks again

 

[drdr]

Well I got and installed the new unit. It works perfectly, wish I had asked the question as to whether it would work before purchasing the ST9100S. A lesson has been learned!
Anyway, thank you all for your assistance.