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

davesparks · Nov 29, 2016

dansk said:
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?

On a Worcester, and some other boilers the external controls need to be connected to the live out from the boiler and not to the switched spur directly.

davesparks · Nov 29, 2016

GreasyWookie said:
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

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

Orange and grey are just either side of the microswitch so will work either way round, but the normally accepted way is to use grey as the switch common and orange as the switched live out.

Can you confirm that the underfloor heating and the boiler are all fed via the one switched fused spur? It sounds like you might have two diffent circuit sports linked together here, which is a very dangerous situation so be very careful until you have confirmed this!

GreasyWookie · Nov 29, 2016

diditrain said:
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 said:
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.

davesparks said:
Can you confirm that the underfloor heating and the boiler are all fed via the one switched fused spur? It sounds like you might have two diffent circuit sports linked together here, which is a very dangerous situation so be very careful until you have confirmed this!

Yes they're both on the same spur. The spur feeds a drayton wiring centre and everything is connected to that.

I think I might understand what's happening now. If the stat commons and ZV greys should be receiving power from LS then The ZRU needs to receive power from there too and only the boiler live connected directly to the spur. The the stats call for heat and ZV orange back to Lr to complete the circuit? I think I effectively had the ZRU live connected to a neutral. I'll be back there tomorrow to try and solve this so I'll let you know how it goes.

GreasyWookie · Nov 30, 2016

Found the problem, the drayton wiring center had a factory fitted link from the live on the spur to the same terminal that I had the boiler LS connected to, so the two lives were crossed. Removed the link, wired the ZV greys & stat commons to the LS, ZV orange to LR, the stats call for heat to ZV brown and ZRU + boiler direct to the spur and its all working perfectly.

Many thanks for all the input, not only did it help solve this problem but I learned a few things about what each wire actually does so I'll no longer be blindly following the wiring diagram... as I discovered not all systems are wired the same and the diagrams are not always 100% accurate.