combi boiler thermostat connection

[Tim Smith]

Hi

I think I have a faulty room thermostat connected to our boiler. I have tried to find where it is connected to the boiler (Vaillant VCW GB240H) but cant find the connections anywhere.

The insuatlion on the cables is quite distinctive so its easy to distinguish between that and any other cables. The only cables I can see are the timeswitch.

Are the timeswitch and thermstat connected together to determine whether the boiler should come on before the signal goes to the boiler or should there be separate connections ?

Tim

[Set Square]

They may well be wired in series - with a single connection to the boiler. In any event, you would only want the heating to be on when *both* timer

*and* stat are calling for heat.

It is, of course, an ideal application for a programmable thermostat - which combines a timer and a stat in a single unit.

[Tim Smith]

Hi,

Thats the idea that Im moving towards, but Id like to know whether the thermostat I have is faulty or not. Much easier to get the purchase req signed off by the financial controller if there is a fault to fix !!!

Ill look again and see if I can find the thermostat cable connected to the timeswtich rather than the boiler but I didnt find it last time I looked.

Thanks for the help,

Tim

[John Rumm]

They may be joined... depends on how it has been wired. Is is a combi or is there a hot water cylinder? If the latter the rooms stat may be paralleled up with the cylinder stat at a junction box somewhere before coming back to the boiler.

[Set Square]

You can test the stat by bridging the live and switched live connections. If the heating works when you do this - but not otherwise - (but with the timer on, of course) that would indicate a faulty stat.

Another possibility is that the timer is duff - which may also justify moving to a programmable stat!

[Dave Plowman (News)]

If you have an external pump, the thermostat will usually just switch that, with the line in being taken from the boiler live - ie after the programmer.

[Tim Smith]

Its a Combi.

Tim