Combi boiler with dual heating zones and 2x programmable stats.

[GreasyWookie]

First post so let me start by saying hello to all!

I'm a plumber not an electrician, nor do I consider myself a heating engineer and would appreciate any help...

What I have is a Worchester combination boiler which is currently hooked up to a Honeywell programmable room stat. We have installed UFH in a newly built extension and the client wants independent zone control so he can have the UFH come on before the rest of the heating. I have installed 2x 2 port zone valves each with its own RF digital 7 day programmable thermostat but I'm having trouble getting my head around the wiring. So far I've added a Drayton wiring center hooked up the wires for the zone valves and room stats as per a standard s-plan system but with the UFH in place of DHW, I presume having programmable stats means I don't need a 2 channel programmer? If this is the case, what do I do with the brown wires coming from the zone valves that normally go to the programmer, are they now redundant or do I need to connect them to the programmable stats? After several hours looking at various wiring diagrams and repeatedly banging my head against the desk I'm none the wiser.

Please Help!

Many thanks.

 

[GreasyWookie]

If this is the case, what do I do with the brown wires coming from the zone valves that normally go to the programmer,

Sorry, brainfart... the browns are linked to the call for heat from the stats. It's the commons for the two stats that normally go to the programmer that are the ones causing my issue.

 

[davesparks]

Commons for the stats would be connected to a permanent live in this case as the stat is doing the job of both the programmer and the stat in a normal system.
In a programmer this link is often made internally, though will occasionally require a physical wire link to be fitted.

 

[Leesparkykent]

commons for the stats and the greys of the valves should be connected to the LS terminal of the boiler.

 

[davesparks]

commons for the stats and the greys of the valves should be connected to the LS terminal of the boiler.

Good point, he did mention it was a Worcester!

 

[GreasyWookie]

Thanks for the replies, that definitely helps, just one small point, the instructions for the zone valves (which are Honeywell btw) show the greys as permanent live and the oranges going to the boiler, so I would guess I do as Leesparkykent says but substitute the grey for orange?

 

[GreasyWookie]

the instructions for the zone valves (which are Honeywell btw) show the greys as permanent live and the oranges going to the boiler

Update...

It's working... mostly. So today I took the info you guys gave me, binned the old programmer, wired in the two new ones with both commons and the zone valve orange wires going to the boilers Ls terminal, both the call linked to the zone valve browns and back to the boilers Lr terminal and hey presto! So now I can ramp up the temp on either of the stats, the corresponding zone valve opens boiler fires and everything is tickety boo right? Not quite... when the UFH pump clicks in the main breaker trips and we lose all power. We're using Polypipe UFH with a 2/3 circuit ZRU, I've installed these before with system boilers in s-plan plus config without any issues, I tried wiring the ZRU to the permanent live from the spur and the brown on the UFH zone valve (a suggestion I found in another thread on this forum) both had the same result - boiler fires runs for a few mins until the UFH pump clicks in (the ZRU prevents this until the water temp reaches 45 degrees) then the breaker trips off. If I disconnect the UFH pump and allow it to run the CH only it works perfectly. I'm stumped.

Any ideas, anyone?

PS. It just occurred to me I should have tried swapping the oranges and greys from the zone valves so it's wired as Leesparkykent says

commons for the stats and the greys of the valves should be connected to the LS terminal of the boiler.

Could this be my issue? If so, why is it working without the UFH pump in play?

 

[dansk]

Where you taking power from for that ZRU? It needs to be on the same supply as the boiler 3amp Fused Spur.

What you doing with the Neutral when your swapping the brown onto the Ls & brown of ZV?

 

[GreasyWookie]

All neutrals and earths are going to the neutrals and earths on the spur and yes the ZRU is on the same spur

 

[dansk]

To confirm:

Thermostat SL > ZRU > Brown of ZV

 

[GreasyWookie]

Thermostat SL > ZRU > Brown of ZV

Yes.

 

[dansk]

Not sure my friend, obviously something is a miss, my guess is the neutral wrong somewhere, maybe in the pump if you wired it, or somewhere else on that ZRU.

Let me know the outcome i would be interested.

 

[Wilko]

... when the UFH pump clicks in the main breaker trips and we lose all power.

Hi - hopefully this won't be too hard to find. Can you advise please what exactly is it that trips? an MCB or an RCD?

 

[diditrain]

LS is a live supply from the boiler to your external controls. LR is a live return to the boiler from your external controls.

 

[davesparks]

Thanks for the replies, that definitely helps, just one small point, the instructions for the zone valves (which are Honeywell btw) show the greys as permanent live and the oranges going to the boiler, so I would guess I do as Leesparkykent says but substitute the grey for orange?

No, the Ls terminal of the Worcester boiler is the live feed to the external controls, so the grey from the valve connects back to that, the orange of the valve connects back to the Lr terminal of the boiler.

Reading your other posts it sounds a bit like you've connected your external controls to the live from the switched spur instead of to the Ls terminal? Unless it is an Ri which does not have this terminal then it's not in accordance with manufacturers instructions and they could refuse a warranty claim based on this.