Replacing analogue timer switch

GristlyEnd

The timer switch for my Ideal Mini S24 boiler is on the blink so I purchased a Horstmann C17 to replace it. I've attached a photo of the wiring for the old switch but I'm a little confused as how it should be wired up to the C17 timer. I've also linked to the installation manual for the C17 below.

Should I just call an electrician or can anyone help me out here?

Horstmann C17 installation manual

nmacc

Well now, this is a little tricky.

Not the wiring you understand, that's child's play. However it's a criminal offence to go wandering about in the innards of a gas boiler if you're not an RGII.

If we assume, for the purposes of legality, that the clock you have illustrated is not part of the boiler, then you could proceed as follows:

The wires attached to pins 4 & 5 of the ZT101 connect to N & L on the Horstmann - polarity not important.
The wire currently going to pin 3 on the ZT101 goes to 2 on the Horstmann; 2 goes to 4 and 1 goes to 3.

By the way, I'm not kidding about the criminal offence bit, so if the clock is in the boiler and you're not an RGII, then leave it alone and go and find someone who is.

However if the problem is that the clock motor has burned out so that it's not turning, the simple solution would be to leave the boiler permanently 'ON' at the existing clock and fit the Horstmann between the supply and the boiler.

GristlyEnd

Thanks nmacc. The ZT101 timer is separate to the boiler.