Combi Boiler Wrong External Programmer - Help!

[David P]

I have a combi boiler, and had to replace the external controller. I got a Tower roomstat, wireless transmitter etc,

However, after it kicking around in the shed for a while I decided to fit it. Now I find it is not volt-free, so would pass 240v to the boiler (which would damage it).

I cant take it back for a refund.

I am thinking I could get the cable that calles for heat to act as the live for the pump. Would this work? Or is there something better I can do? I really dont want to waste thr =A360 the damn thing cost.

[Roger Mills (aka Set Square)]

You could fit a relay between the programmer and the boiler - using the programmer to switch the relay coil, and using the relay's volt-free contacts to switch the boiler. Something like

should do. Make sure you get the version with a 240v (and not 12v) coil.

[Dave Plowman (News)]

Simply add a relay. Something like this - although it's a double pole job.

[David P]

Is that what a relay does?!

Thanks guys, I will check that out.

[Dave Plowman (News)]

In its most basic form it is simply a switch which is operated by a solenoid. And the switch is electrically isolated from that solenoid in most cases. The solenoid can be specified for near any voltage, AC or DC. And the switch also rated for near any voltage or current. Many relays have multiple switches or contacts that operate at the same time but may be connected to different things.

[David P]

Ok Dave that makes perfect sense now!

So how do yoy actually connect wires to this relay?

Maybe I should to maplin and look at some of this stuff.

[Dave Plowman (News)]

There are many different types available but most have a plug in base as an accessory which you make solder connections to. An easier way - but a bit more expensive - would be to get a plug in type with base which has screw connections. See:-

Maybe I should to maplin and look at some of this stuff.

Maplin's range of this sort of stuff is a bit limited these days and the shops often don't stock it, so mail order only.

TLC and other electrical wholesalers stock plug in octal relays with screw terminal bases but are likely to be more expensive than electronics suppliers.

[David P]

Thnaks again Dave, I have ordered the above item. Finger crossed!

[David P]

Thanks Dave, I have ordered the relay and will let you know what happens!

[John]

However, after it kicking around in the shed for a while I decided to fit it. Now I find it is not volt-free, so would pass 240v to the boiler (which would damage it).

I cant take it back for a refund.

I am thinking I could get the cable that calles for heat to act as the live for the pump. Would this work? Or is there something better I can do? I really dont want to waste thr £60 the damn thing cost.

What boiler is it? Some have a 240 volt option (GW etc)

[Ed Sirett]

In the worst case you would have to use a relay unit. But you may well find that the 'volt-free' contacts are in fact main voltage.

[David P]

Oh the volt free contacts in the boiler really are not mains voltage!

Until the relay arrives, I have fed the switched live from the stat to the live on the inbuilt CH clock on the boiler (Ravenheat, yes I know, dont even go there..)

Seems to work OK.