S-plan plus: second zone depends on first?

[primping-swashing]

We just moved into a house that has two heating zones. Downstairs has a Honeywell ST6400C programmer and a wall thermostat, upstairs has a programmer/thermostat Honeywell CM67. There are two loops and two valves, but it seems the upstairs zone cannot heat if the downstairs zone isn't already heating. That is, unless the CH light on the ST6400C is on nothing happens upstairs. I'm trying to understand all the wiring now (of course nothing is labelled) but a crude check with an AC power pen shows that the CM67 upstairs doesn't get power until the ST6400C downstairs turns the heating on.

1) is this a common configuration? It seems a bit weird to me and we'd like to be able to heat the upstairs independently of downstairs.

2) if this is common how would it typically be implemented? I'm guessing something like the attached pic but this is my first foray into heating systems so I'm not sure what's common.

3) assuming it is configured like 2), could I just move the live leg of the upstairs controller to a permanently live supply to resolve my problem?

 

[jackthom]

From the checks you’ve made it does look as if that’s how it’s wired up.

As you say, I would try providing the upstairs programmer with a permanent live and see if it all works the way you want.

 

[BlueLoo]

Check all of the wiring including the boiler and make sure it is all correct.

The equipment manuals will show you how to wire it all.

Don't assume this is the only problem.

Easy enough tbh. Just be methodical.

 

[ianmcd]

No you are confused , you have a remote room thermostat, it sends a signal to the receiver , which is wired to the corosponding zone valve, it is the receiver that controls what the zone valve does

 

[primping-swashing]

No you are confused , you have a remote room thermostat, it sends a signal to the receiver , which is wired to the corosponding zone valve, it is the receiver that controls what the zone valve does

What is the receiver you describe here? The ST6400C downstairs has only connections for live/neutral/earth and HW+CH on, so that can only control the HW and downstairs CH zone valves. The CM67 upstairs has only two wires so presumably also controls a single zone valve upstairs (and, as far as I can tell, this feed is only live when the ST6400C has turned on CH). I can't see how the thermostat upstairs can "send a signal" beyond turning on a zone valve.

I’m going to poke around with the wiring when I get a chance.

 

[fezster]

Most likely, the ST6400C programmer is being used for both u/s and d/s, but the zones themselves are being heated independently via the room thermostats. So you are still getting independent control, you just need to use the programmable thermostats to control timings, rather than the programmer itself.

You could change to a 3 channel programmer or add an additional single channel programmer, but it's unnecessary if your thermostats are programmable.