Combi Boiler with Appliance switch

[sonix]

Hi All,

I've got a pretty standard combi-boiler (valiant) and controller set-up. I'm thinking of automating the heating by putting in a X10 appliance switch to control the power going to the boiler/controller, and therefore automating the heating.

I was wondering if this is a good idea, could there be issues with swtiching the power on and off to the boiler?

sonix.

[SensibleHeatUK]

you should check and see what provision there is for control of the boiler by external devices - most modern boilers have a permanent supply with control achieved by switching a second supply on dedicated terminals within the boiler. In the boiler wiring information this will be shown as terminals for connection of an external thermostat or time clock (more often than not there is a factory-fitted link between these terminals that you remove when wiring in the new controls).

As your boiler is a combi then it will definately have this kind of setup. To add in control of the heating via X10 you would wire the appliance module in series with any other controls you want to keep in circuit (such as thermostats) and in parallel with any other controls you might want to also operate the boiler (such as another timeclock for standard control).

This way you do not interrupt the permanent supply to the boiler, if you did you could not have hot water when switched off and it may also prevent other functions operating such as the timed pump overrun whenever the boiler stops firing - the overrun ensures that any residual heat is removed from the heat exchanger which could otherwise cause te boiler to trip out on high limit or maybe even cause damage to the heat exchanger.

[toscal]

Totally agree with Sensible Heat (by the way I have sent you a PM)
As a word or warning, some combi boilers use low voltage for the control. I have a bosch boiler and this uses plus and minus 12V for the control. But the thermostat has provision for a contact closure to put the heating in what they call vacation mode. So check your thermostat, if it has this feature then you could use a Universal Receiver Module so you could controll the heating via the contact closure.
And as sensible said many combi's have a link on the ciruit board, and once again the Universal Receiver Module may work for this.

[sonix]

Thanks for the quick reply, seems there is a little more to it than I thought. I've been looking at the wiring diagram on the Valiant website, but to the honest it's beyond me (I'm not an electrician), but sounds like it's may be possible in the manner you mentioned.

I'll continue to look into it.

Thanks again.