Combi Boiler Central Heating Only Works When Hot Water is on

Postby Rowlett » Mon Jan 16, 2017 11:40 am

Hi All,

i don't know much about central heating so if i miss some obvious information needed let me know :-)

i moved into property 6 months ago (coming from 1st property which has a combi) and i know the central heating/boiler is old and will be replaced when i get the cash but as it's working and for now i decided to replace the controls to lower bills a little because as it was setup, we can only have the heating on when the hot water is on (no TRVs either btw! lol) - i was hoping to replace programmer to have independent control of hot water + central heating as we barely use hot water, a shallow bath every other night for the little one and 2 showers at night, all appliances i have only need cold feed.

i've bought a tado smart thermostat + extension kit that has capability to control heating and water independently and it's replaced the Switchmaster400 programmer + British gas RS2 thermostat. the switchmaster400 only had controls of "Central Heating + Water or Hot water only" no central heating only and then "timed,off,constant"

i've replaced it all fine and works how it used to however to control them independently i believe extra wiring needs to be done? current wiring only had CH ON and HW ON connected.... i can also connect the hot water tank thermostat to the extension kit too i believe so it will show hot water tank's current temp?

i have a Baxi WM51/3RS boiler (old i know!), a hot water tank and tank in the loft... i believe my system is a Gravity fed Y plan with 2 valves? really not sure.

is it just the case of additional wiring from terminal block in airing cupboard or will it be more work than that and rewiring at boiler needs to be done or not even possible with current setup?

please see pics for more info and wiring description below





upstairs terminal block in airing cupboard - i've labelled cable going to programmer/extension kit the others are:
x2 Grey cables, top right on pic are coming out of floor from boiler
x1 top left white cable just in view is from red cased (central heating pump/valve?)
x1 black cable is from black cased pump/valve? that connects to water tank (hot water pump/valve?)
x1 white cable bottom right in pic is from the hot water tank switchmaster thermostat

Any help would be much appreciated! :-)
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