Underfloor heating + rads has left me stumped!

[electromonkey]

Hello all

I am not ashamed to admit that I have been left scratching my head over a central heating system that I have attempted and failed to wire correctly.

There is a combi boiler supplying a ground floor under floor central heating which is broken in to three zones with a stat and manifold per zone. There are then rads on the first and second floors. The rads and underfloor are supplied by two motorised valves.

I have the wiring diagram for the installation of everything and have checked and double checked it so I know it is correct in relation to the manufacturers instructions. Where the wheels come off is where I have a four core and earth going to the programmer for the under floor heating, a three core and earth for the radiator programmer and a twin and earth back to the boiler for which I have no wiring diagram. The wiring instructions for both programmers have no instruction regarding this type of central heating system. My customer insists that the programmers are the correct ones. I have phoned the tech support for these programmers who basically told me that I would need to "work it out" to get it to work!

I have blown 2 2.5A fuses in the boiler already and am not fancying having to replace the pcb so is there a wiser person out there who can help me? Do you think the programmers may not be compatible and if not could you recommend ones that are please?

Thanks in advance.

Electromonkey.

 

[Timbo_1975]

Ok, this is what I usually do with these systems which are 99% of the time a system boiler + unvented cylinder, so adapt where necessary for a combi and no cylinder. I wire as per usual S-plan system+1 extra zone:

You'll need 2 x 5core multi's from programmer to a wiring centre at the motorised valve location, and 1 multi from there to the UFH controller location. UFH thermostats will need a 4 core multi to each one from the UFH controller location.

3 channel programmer - HW, RADS, UFH. (although you could use a regular 2 channel combining the heating)
3 x motorised valves in my case.

1 valve supplies the rads. As per usual. Call for heat via the room 'stat located on the landing.

2nd valve supplies water to the UFH manifold. Here you have the UFH contoller. Treat this as its own separate system. This needs a mains supply from the FCU and is live all the time the power is on. It also will have a no-volt contactor which is the call for heat and is wired via the motorised valve back to the boiler. The various room stats come back to the controller which opens the electrovalves for the different rooms as needed. The controller fires up its own pump when one or more room stats call for heat *after* the relvant valves have opened.

Does this help??? Admittedly all systems are different, and can get pretty complex pretty easily. You need to break it down into the separate parts to make it easier to understand.

 

[electromonkey]

Thanks Timbo

You lost me at "Ok"!!! LOL

I think I know where you are coming from with this.

If I PM you later, would you mind taking a look at a couple of diagrams for me just so I can be sure I'm on the right path please?

I think my customer is about to freak out on me over this. The plumber washed his hands of it, leaving little old me to fend for myself.

 

[Timbo_1975]

of course.

 

[electromonkey]

Here's the image of the manufacturers instructions which I have stuck to.

 

[Dunc]

If you've blown the fuse in the boiler twice i think you've created a live to neutral short across the boiler 'thermostat connections'. If you let me know what boiler model you are using i may be able to help. Am i right in saying that there are 3 zones on the UFH manifold with a room stat on each zone operating a actuator? Need a bit more info i think if you can give it.

 

[electromonkey]

Hi Dunc

Yeah, 3 zones, 3 manifolds and 3 stats. It's a worcester boiler. I think it's the greenstar one. I thought as much about a LN wiring fault to blow the fuse.

 

[Dunc]

Okay, does the underfloor manifold have it's own electronic wiring centre that looks like this? Just trying to get my head round everything first as the diagram in your post doesn't show quite enough detail.

 

[Dcf]

i had a danfoss one that the plumber left me right in the cack with and managed to suss out that the connection for the pump on the wiring centre i thought was l-n was actually l and sw wire. problem sorted could b why you are blowing fuses

 

[electromonkey]

Here's the make for the wiring centre. http://www.heatmiser.co.uk/web/index.php/underfloor-heating-controls/underfloor-heating-wiring-centres

The programmers however are a screwfix cheapo make, Hortsmann.

 

[Des 56]

ref Blowing fuses on the combi boiler,not a good thing to happen

Has there, by any chance, been a mains voltage applied via the no volt contacts of the worcester that has caused the boilerl printed circuit to give up the ghost



What is the result if you apply power to this combi with no external control ?

Is the combi thermostat no volt link removed and the external circuit routed correctly ?

 

[Timbo_1975]

I agree the wiring diagram is rather basic although it appears correct. Most people would have problems getting it to work first time!!

We really need abit more info as to how the UFH controller is wired- looks like it has call-for-heat / live on brown, neutral on grey, and sw-live on black. This then opens the valve, which links the two Boiler thermostat wires, one is live, the other is call-for-heat. Thus this fires up the boiler.

Check that the motorised valve Orange & Grey wires are volt-free when disconnected.

If the UFH room stats are the digital type the controller needs a permanant live to remember their settings. However, missing this out wont cause the fuse popping!

 

[Dcf]

do the greenstar combis not have a connection on them for external stat/ programmer connections.the heat miser output to the boiler is live/ sw live. i hate floor heating. it is always a total james to connect into systems with rads especially with a combo boiler

 

[electromonkey]

I'm going to the job again today folks so I'll take my laptop with me and upload some more snaps this morning.

Cheers

 

[Dunc]

Looking at it the first thing worth checking is that you aren't putting a L-N short across the boiler control terminals. The switch live (SL) on signal to the boiler should be connected to LR at the boiler which is a 230V contact. The other connection going to the control box will be via the LS connection. Hope this helps.