SOLVED! - Central heating only comes on if hot water is set to on

[oakc]

Hi all,

moved into house 6 months ago and central heating system is old and i know boiler needs replacing (Boiler is a Baxi WM51/3RS) but it's working for now and i will do so when i get cash (aiming for next 12/18 months) i "believe" it's a gravity fed Y Plan 2 Valve system? not really sure. have hot water tank in airing cupboard and cold tank in loft.

i've replaced the programmer and thermostat to give us more control and to lower bills a little in the short term.

Original was:
Switchmaster400 Programmer
British Gas RS2 Thermostat

i've replaced it with a tado smart thermostat + extension kit and it's working how it use to as the switchmaster400 could only have "heating+ water" or "water only" there was no heating only switch.

To be able to control them independently i believe additional wiring needs to be done? just not sure what

the tado is capable of independent control and i believe i can even wire in my hot tank thermostat to get current temp? (not really bother if can't just want independent control atleast)

any help would be much appreciated!!!!

Current wiring had CH ON & HW ON + N L + Earth nothing else. attached pics of setup + wiring.

wiring in terminal block casing
x1 white cable, top left on pic goes to red cased pump/valve, which i believes the central heating valve?
x2 grey cables, top right on pic comes out of floor from boiler
x1 black cable, bottom left on pic goes to black/dark blue cased valve which is connected to hot water tank (believe this is hot water valve?)
x1 white cable bottom right comes from the hot water tank thermostat (switchmaster)

 

[oilhead]

You probably need additional plumbing as well as wiring. You probably have gravity DHW. It needs to be fully pumped.

 

[oakc]

Ahhh i was afraid of that - how can i tell if its gravity DHW or fully pumped? Thanks for quick response.

 

[Agile]

it is possible that the wiring is capable of separate control. Certainly your three port "Y" plan is.

Unfortunately the photo of the wiring centre is not very clear.

I would first like to see where the wires from the cylinder stat. That should be set to 60 C.

Tony

 

[stem]

Don't worry it's a Y Plan The clue is the presence of a 3 port motorised valve.

Untitled

• stem
• 1 Apr 2010
• 8

Everything else required seems to be present, but it would have been easier if you had got it working properly before adding the Tado.

The motorised valve contains a microswitch that controls the boiler when central heating only is selected. If this fails, the valve moves to the heating only position but doesn't operate the boiler, when hot water is required the boiler comes on because in this mode the boiler is operated by the cylinder thermostat.

But this is just one possible solution. I suggest that you check your wiring first. The schematic on this website is very helpful. Click on the Y Plan schematics to see what should happen when.

 

[flameport]

old and i know boiler needs replacing

'Old' and 'needs replacing' are not necessarily the same thing.

Throwing away a perfectly good and working older boiler just to get a more efficient new one does not automatically mean you will save money.

 

[oakc]

it is possible that the wiring is capable of separate control. Certainly your three port "Y" plan is.

Unfortunately the photo of the wiring centre is not very clear.

I would first like to see where the wires from the cylinder stat. That should be set to 60 C.

Tony

I can try and upload clearer pics but:


Thermostat cabling:
Red cable is in terminal 7
Orange cable in terminal 8
Yellow cable in terminal 9

Terminal 7 has:
Red cable from thermostat
Black cable going to programmer (T3 on programmer - HW ON)

Terminal 8 has:
Orange from thermostat
Orange from black cable (hw valve?)
Brown from central heatin valve
Yellow from boiler (grey cable coming up from floor)

Terminal 9 has:
Yellow from thermostat
Grey from black cable (hw valve?)

 

[oakc]

Don't worry it's a Y Plan The clue is the presence of a 3 port motorised valve.

Untitled

• stem
• 1 Apr 2010
• 8

Everything else required seems to be present, but it would have been easier if you had got it working properly before adding the Tado.

The motorised valve contains a microswitch that controls the boiler when central heating only is selected. If this fails, the valve moves to the heating only position but doesn't operate the boiler, when hot water is required the boiler comes on because in this mode the boiler is operated by the cylinder thermostat.

But this is just one possible solution. I suggest that you check your wiring first. The schematic on this website is very helpful. Click on the Y Plan schematics to see what should happen when.

The old programmer wasnt capable of heating only which is why i was/am replacing it? Thanks for schematics though

 

[oakc]

'Old' and 'needs replacing' are not necessarily the same thing.

Throwing away a perfectly good and working older boiler just to get a more efficient new one does not automatically mean you will save money.

Its british gas who keep telling me parts cant be purchased anymore and its off the charts in effeciency...well its G Rated anyhow... boiler has been reliable so far, does take a while to heat the house up dunno if its because boiler power or microbore pipework to rads? but no complaints so far **touch wood**

 

[oakc]

 

[oakc]

i don't know if those pics help more?

 

[oakc]

looking at the plan stem sent of wiring i'm just missing cable going from terminal 7 to HW off on programmer... am i right? surely that's not all it needs?

 

[oakc]

i also didn't have cable in term 3 on room stats it just had L and 2

 

[oakc]

i think i'm confusing myself now lol

 

[stem]

The old programmer wasn't capable of heating only which is why i was/am replacing it?

Ah, OK thanks for the clarification, however the schematics will still apply, you will need to use the following terminal at the Tado extension box.

1. Hot water off (goes to grey wire motorised valve)
3. Hot water on
4. Central heating on (goes to white wire on motorised valve)

i also didn't have cable in term 3 on room stats it just had L and 2

Not all thermostats need three wires, some don't have a neutral connection, they just have two switching wires.