Honeywell st669 to st9400c

[rumel1993]

Hi wondering if someone can help me

This was my existing wiring.

What I have read there at no links needed.

I wired the st9400c
As the following

However my central heating doesn’t come unless the water is on.

The previous set up was
Central heating can be on without water
And vice versa
Hot water without central heating

Thanks

 

[Deleted member 267285]

Looks like you may have a Y plan, on the original ST699 there was a link to Hot water off.

 

[rumel1993]

Would it possible to have the same system on this one?

So either have one on or off

Thanks

 

[Deleted member 267285]

Not entirely sure as newish to programmers and wiring. Might be able to put a link it but not 100%

 

[rumel1993]

appreciate it, any help is better than nothing.

Thanks

 

[RandomGrinch]

The previous set up was
Central heating can be on without water
And vice versa
Hot water without central heating

Your existing controller is wired in a way that if C/H is turned on, The water will also heat. The two are not independent.

@CBW, does this suggest a gravity system?

I don't know an easy way to replicate this with the ST9400c, apart from manually turning on both heating and hot water.

Alternative controllers can replicate how the ST699 functions.

 

[Deleted member 267285]

Your existing controller is wired in a way that if C/H is turned on, The water will also heat. The two are not independent.

@CBW, does this suggest a gravity system?

I don't know an easy way to replicate this with the ST9400c, apart from manually turning on both heating and hot water.

Alternative controllers can replicate hiw the ST699 functions.

I did ponder if a gravity system, but I’ve never really understood the wiring on them. Someone else’s brains for this I’m afraid.

 

[RandomGrinch]

 

[DP]

Easier to fit a single channel timer and a programmable Roomstat.
Thus you will get the operation you desire

 

[RandomGrinch]

Or smart stats could be considered?
Nest can be setup in the same way as the ST699 and Hive has a gravity mode.

However, given the current systems limitations, would it be worth thinking about a system upgrade?

 

[rumel1993]

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

 

[RandomGrinch]

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

Yup, sorry!

Although there is mention of a 'mini programmer' mode in the manual. However, I don't know what functionality this gives...

EDIT: Some further info...

 

[rumel1993]

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

 

[RandomGrinch]

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

Yes, that's what happens with a gravity system.

It's what happened with your old system as well, but because of the way it was wired, you wouldn't have noticed it.

As in my third diagram in post #8, with Hot water set to off and heating set to on, power is still being provided to both the heating and hot water circuits.

 

[rumel1993]

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

I remember the water out of the tap would get Luke warm but not hot like when I put the hot water on.