Another Hive installation. Please help

[Petethebodger]

Hi all,

I would like to replace my current timer and thermostat with the Hive heating and hot water. My current timer is a Landis and Staeffa, boiler is a potterton netaheat ( very old) with a thermostat in the hall.

Wiring the hive seems straight forward as connections seem the same, however my issue is with the thermostat. it has three wires in it. There is no wiring box so an I to assume the thermostat is wired directly to the boiler? I ask this as I need to remove the wiring for the thermostat.
Thanks, I’ve attached a few pics for reference.

 

[ericmark]

It is possible that the hive will fit on the old timer base plate, however before you can work out how to remove old thermostat you need to know what system you have.

Three main systems are:-
Y Plan which has three port valve.
S Plan which has two x two port valves.
C Plan often no valves but there are three versions of C Plan.

There is a W Plan etc but your unlikely to have that.

Often there is a wiring centre, that's a heating guys name for a junction box, and often the programmer (timer) feeds the thermostats, then the thermostats feed the motorised valves, and the motorised valves feed the boiler.

 

[Petethebodger]

Thanks I believe it’s C plan system.

 

[stem]

my issue is with the thermostat. it has three wires in it. There is no wiring box so an I to assume the thermostat is wired directly to the boiler? I ask this as I need to remove the wiring for the thermostat.

There should be a diagram inside the old Honeywell thermostat lid. Something like below, yours may be slightly different as it doesn't have terminals 5 and 6. So, you are only interested in terminals 1, 2 and 3

If your thermostat has the same wiring connections, then the terminals can be identified as below, if they are different, post back their details.

1. Live (red wire in your case)
2. Neutral (blue wire in your case)
3. Switched live (yellow wire in your case)

The cable should be traced from the thermostat back to its origin' Unfortunately there are a vast number of possibilities as to where that would be, as it depends upon many factors including the type of system, the layout of your home, personal preferences of the original installer, if the system has been modified at any point etc., You may need to trace it physically.

When you find the origin of the cable:
1. Make a note of where the red and yellow wires are connected
2. Disconnect all of the wires and remove the cable
3. Insert a wire to link together the two terminals where the red and yellow wires have just been removed from so that they are electrically connected.

 

[ianmcd]

You will have a wiring centre somewhere, easiest way to find it, is follow the cable from the motorised valve(s) , or easiest way the wires in 1&3 of the thermostat get joined together and isolated and the Neutral is isolated then tucked safely away, not ideal, but will work untill you find the wiring centre, (might be below the floor)

 

[ericmark]

The old C Plan would be some thing like this

the connection block can be wired using different numbers but some where normally a wiring centre with that connection block, the time controller can't turn on the pump without boiler, but can turn on boiler without pump, so with pump central heating (CH) works, without pump only domestic hot water (DHW) and there are turn buckles and dip switches insider the programmer (time controller) which stop you being able to select CH without DHW. There is in Hive a software option which does the same, the problem is DHW is pure time, not a problem in winter, but a bit hit and miss in summer, so there have been two upgrades from the original plan.
This plan includes a thermostat so in summer the boiler only runes when required, and in summer you can control DHW temperature, in winter DHW temperature like other system is same as boiler, I don't think hive can be configured to work with this, but will stand to be corrected.
Then next stage was add a motorised valve this system allowed the DHW to be set to lower temperature to CH not sure if Hive can work with this, it seemed great but the latter system could cause problems with some boilers as there was no route for the water to cool as boiler turned off, I am an electrician not a plumber or heating engineer, so my knowledge is limited.

The big problem with central heating is there is no cable colour code, even found green/yellow wires being used for line with some systems, may be wrong, but still done, so one has to be really careful. In my own house fitting Nest to C Plan I identified and re-used cables, but wired from scratch, as it became apparent there were multi errors, and one can end up chasing ones tail.

But job one is find that wiring centre/junction box, often it is a socket back box with a blanking plate.