Hive Dual Channel Unvented Cylinder

[Allum1989]

Apologies if this has been discussed before.

So we have had an indirect unvented cylinder (Joule Invacyl) fitted which is heated by a Worcester Greenstar Ri boiler in a Y plan configuration. We have had a hive dual channel installed a week after the cylinder.

The heating stopped working after the cylinder was fitted but hot water was fine. We thought it was an issue with the old programmer so just waited for hive to be installed and it didn’t solve the problem, diagnosed it as the Honeywell 3 port valve which was swapped and the heating still didn’t work but hot water does. The valve now moved to the right position but the boiler and circulator pump don’t kick in unless there is a call for hot water. After much head scratching, testing with the multimeter and studying of heating wiring setups I have realised it’s because we have the hive set to hot water always on so there is never voltage going down the hot water off wire which is what supply’s the boiler with voltage.

I want the hot water to just be set to always on in the hive and just have the cylinder stat manage it by kicking on when it dips below the set temperature but this means I can never turn the heating on as the hive receiver is never sending voltage down the hot water off line.

My thinking was to link the hot water call wire from the hive receiver to the hot water off wire in the wiring center. Is this a viable workaround to this or will this cause issues? Is there another way to make this work properly?

Thanks for your help.

 

[ericmark]

With Y Plan, DHW supplies the boiler with a signal to run from the cylinder thermostat, but the CH gets the signal from the motorised valve.

The motorised valve is an odd device, the grey wire turns the DHW off, by motoring the valve all the way across, if not connected the DHW will get as hot as the CH water, and it will allow hot water to return to the boiler reducing the boiler's output, but the CH will still work.

If the micro switches fail in the motorised valve that can stop central heating working, latching the valve with the bleed lever on the valve can sometimes get the CH working, but that also means in the summer the radiators can get warm.

The Hive

does not need the original thermostat. Note the bridge shown on this diagram. There are no standard colours or order of wires for most of the central heating, but the motorised valve has the wires as part of the device, so that is the only thing colours are correct with, so look for the orange wire.

Once you have worked out the wires to terminal 8 on the diagram shown, you can work out if the orange wire becomes live. But the resistors and diodes in the valve, means you need a meter, as you can get some odd results.

 

[Allum1989]

Hi Eric

Thanks for your reply. The orange wire is going live to 240v when the valve first moves over but then doesn’t stay live. I have replaced the entire valve and also the head of the valve as I first thought the new valve was faulty.

I tried what I said in the post above and linked the wire from the CH on going into the valve, which stays live at 240v, to the CH off wire in the wiring center and that works fine now with the heating coming on but if the heating comes on when the HW is called from the cylinder stat it then doesn’t turn off unless I manually turn the stat down to end the HW call. The Valve also stays all the way over until I end the HW call from the cylinder stat.

I tested the hive receiver and it sends 240v out down the HW off wire when I turn the HW off in the hive and the heating works then but like I said I want to be able to just leave the HW on and let the cylinder stat manage it.

 

[flameport]

indirect unvented cylinder (Joule Invacyl) fitted which is heated by a Worcester Greenstar Ri boiler in a Y plan configuration.

Unvented cylinders on Y plan are entirely non-compliant and should not have been installed.

There is an ugly fix which involves an additional 2 port valve for the cylinder, but the proper solution is to convert to S plan, and that is what should have been done when the cylinder was installed.

 

[ericmark]

I know @flameport knows his stuff, so if he says should not have a three port valve, then no point of trying to work it out any further.

 

[Allum1989]

Yeah it has the in line 2 port valve on the HW side so it’s fully compliant. You’re right it’s an ugly fix but it’s compliant.