Heating system wiring - Heating only works with HW on?

[Mike Knapper]

Hello,

I am looking for some professional advice reagring my heating system, The Heating will only come on when the hot water is on... Its been like this for 4 years since i bought the house, i assumed it is design that way but recently someone told me they should always be able to control seperately and likely its a wiring issue or the 3 port valve isnt working correctly. So recently i bought a Nest and swapped my Drayton LP522 programmer and Heatmiser TRTS thermostat, to do this i took the room thermostat off and connected the Switch live to Live to bypass the thermostat and swapped the Drayton programmer for the Nest Heat link.

The Drayton had N, L, 1 (HW off), 2 (CH off), 3 (HW on), 4 (CH on)

N had 240V black from the spur and a blue from the 4 core connected, L had red from Spur connected, then red from 4 core to 3 and yellow from 4 core to 4, earths connected together. No connections on 1 or 2.

I changed this wiring onto the Nest with N/L to N/L and 3 (HW on) to 6 and 4 (CH on) to 3 with a link from live to 2 and then onto 5.

The nest works great but once again only when the hot water is on/or boosted...

To try and resove the wiring is it is that i have chased all the wiring in the airing cupboard and created the attached wiring diagram.

Please can someone have a look and see if anything is obvious? The Valve is a EPH B322PF.

Thanks

Mike

 

[ianmcd]

you need a connection to 1 HW off and this is joined with HW satisfied from the Cyl stat, these are connected to the grey wire on your 3 port mid position valve

 

[stem]

Here's your diagram with the missing wire added. I assume the boiler is connected to the lower of the two cables marked "240V cable"

So recently i bought a Nest and swapped my Drayton LP522 programmer and Heatmiser TRTS thermostat

@ianmcd it won't be terminal 1 though, OP says this is a Nest and 'Hot water satisfied' on a Nest Heat link is terminal (4)

The old thermostat doesn't need to be left in place, or linked out. Because according to your diagram you have connected Nest 'heating call for heat' directly to the motorised valve brown wire so by-passing the original thermostat wiring completely. Which is fine, but it means that the original thermostat and its wiring can be removed.