Boiler side connections for UFH wiring centre

[RuraidhBoy]

I've been away from electrical work for about 30 years so I'm not familiar with all the names and terminology that's been introduced over the years.

We're having UFH heating installed. Plumber is doing the pipework, s-plan etc and I'm installing a Heatmiser wiring centre. for the electrical side. Wiring everything up as per the attached diagram is pretty straightforward but I'm looking for confirmation where the boiler side connections go and looking for some help from those with experience. It's an oil boiler by the way and it's all the different terminology for volt free, dry contacts, etc that's confusing. COM/NO for some boilers, Ls, Lr or L, S/L etc

I asked the boiler manufacturer for advice, but because it was a 3rd part wiring centre, they didn't want to give advice and told me to consult the installation manual and work it out from there instead.

So, the heatmiser is a volt free connection that goes to the "boiler enable" terminal but there is nothing labelled as boiler enable. From the boiler manual (images attached), there is a COMN4 terminal with a jumper to be removed. I presume that Ls form the heatmiser wires into L(5) on the boiler and Lr wires into S/L (4) on the boiler.

For the dip switches, I need to set the demand mode to "switched live" and dip switches 6 = OFF, 7 = OFF, 8 to OFF

From what I can gather, "volt free" isn't an actual supply, but is a relay voltage between 0-230v that is a switch that tells the boiler to start heating.

Have I got this right or not? Just want to be sure so that I don't send a voltage that fries the main circuit board.

 

[brianmoooore]

You are correct that 'volt free' means that the heatmiser relay contacts do not connect to any of the other internal wiring of the unit.
These UFH wiring centres are simple devices that look much more complicated than they are. I suggest that you take the circuit board out of it and spend a couple of hours tracing out its circuit, and you'll see what I mean.

 

[RuraidhBoy]

You are correct that 'volt free' means that the heatmiser relay contacts do not connect to any of the other internal wiring of the unit.
These UFH wiring centres are simple devices that look much more complicated than they are. I suggest that you take the circuit board out of it and spend a couple of hours tracing out its circuit, and you'll see what I mean.

Thanks, but I understand the heatmiser easily enough and can wire into it no problem at all (I was a electronics/semiconductor engineer). There's no need for me to take the heatmiser apart.

My query is about the boiler side terminal connection - more specifically the naming. Other boilers I've seen have a terminal connection on the main circuit board labelled "Boiler enable or Heat enable" but this boiler doesn't. This boiler terminal has a terminal labelled as COMN4 and I just need to know that this is the equivalent to a heat enable terminal.

 

[brianmoooore]

I've been an electrician all my working life and also a plumber/heating engineer (oil only) for the last forty years, and I've never come across an oil boiler with anything that could be described as a circuit board.
What boiler is this?
Not at all certain, so might need some experimentation, but my first guess would be to connect the volt free terminals in place of the AC thermostat jumper.
Don't see COMN4 on the boiler diagram.

 

[RuraidhBoy]

I've never come across an oil boiler with anything that could be described as a circuit board.

You've never came across a circuit board on a boiler? The green panel inside the boiler with all the microchips, capacitors, relays electrical connections is the main circuit board. I've never seen a boiler that doesn't have one and a boiler can't power up without one.

Image bolier1.png is the block diagram for the circuit board. COMN4 = terminal d.

"my first guess would be to connect the volt free terminals in place of the AC thermostat jumper."

So, presumably, this is the call for heat terminal?

 

[DefyG]

d5(L) to Ls and d4(SL) to Lr

Volt Free means zero volts on relay contacts until you connect to it (upto rated voltage). Connect 12v one side, it will switch 12v on the output. Connect 230v one side, it will switch 230v to the output, or any voltage in between!