replacing a Honeywell st7100 with a st9400c wiring

[simzep]

Hi I'm looking to replace my old Honeywell st7100 programmer with a new st9400c.The connections on the st7100 are to 8(HW on) 5(CH on).A link between com 6 and com 4. A link between Live and com 3.And the usual live and neutral connections.Would I be right in thinking that I just need to connect old 5 to the new 4 (CH on) and the old 8 to the new 3( HW on).Plus the live/neutral connections.I have taken a pic of the wiring on the old st7100 link below...Appreciate any help,many thanks ,,Simon..
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[D_Hailsham]

Would I be right in thinking that I just need to connect old 5 to the new 4 (CH on) and the old 8 to the new 3( HW on). Plus the live/neutral connections.

Yes.

 

[stem]

You are correct. The 'linking' wires you have presently are not required with the st9400c as they are made internally.

You don't say what sort of system that you have it connected to, however, the simple nature of the wiring and its age, suggests to me that it may be a gravity hot water system, with just pump control for the operation of the heating. (ie devoid of motorised valves) If it is, because of the mechanics of the system you will not be able to have the heating on without the hot water and will need to configure the programmer to work in this way.

 

[D_Hailsham]

the simple nature of the wiring and its age, suggests to me that it may be a gravity hot water system,

It could also be an S Plan!

 

[simzep]

You are correct. The 'linking' wires you have presently are not required with the st9400c as they are made internally.

You don't say what sort of system that you have it connected to, however, the simple nature of the wiring and its age, suggests to me that it may be a gravity hot water system, with just pump control for the operation of the heating. (ie devoid of motorised valves) If it is, because of the mechanics of the system you will not be able to have the heating on without the hot water and will need to configure the programmer to work in this way.

It Is a gravity fed system..The system does have two motorised valves one c/h and 1 h/w..I assume this would mean that each can operate independently?

 

[stem]

Yep if you have motorised valves you can run the central heating on its own, no need to change the programmer functionality

 

[D_Hailsham]

It is a gravity fed system

No it's not, it's a fully pumped system. "Gravity System" refers to heating the hot water tank by natural circulation (hot water rises, cold water falls) from the boiler

The system does have two motorised valves one c/h and 1 h/w. I assume this would mean that each can operate independently?

You have an S plan, as I thought. Yes, each system can work completely independently of the other.

 

[simzep]

Yep if you have motorised valves you can run the central heating on its own, no need to change the programmer functionality

Thanks very much to all for their help.I'm feeling a lot more confident about tackling the job now.

 

[simzep]

It is a gravity fed system

No it's not, it's a fully pumped system. "Gravity System" refers to heating the hot water tank by natural circulation (hot water rises, cold water falls) from the boiler

The system does have two motorised valves one c/h and 1 h/w. I assume this would mean that each can operate independently?

You have an S plan, as I thought. Yes, each system can work completely independently of the other.

Always learning,,,cheers...